Naked Science Forum

Life Sciences => The Environment => Topic started by: Mootle on 16/10/2011 16:41:42

Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 16/10/2011 16:41:42
Hi folks - I've made a bit of an animation for a new type of hydro power renewable energy system. Hopefully, this will show how it works but it would be good to know if I've managed to get the idea across. Please let me have any comments (good or bad,) relating to my Buoyancy Engine idea so I can focus emphasis in the right places for future videos in the series.

http://www.youtube.com/watch?v=q2pUlbusnXo (http://www.youtube.com/watch?v=q2pUlbusnXo)

Many thanks

Mootle
Title: Re: Will this buoyancy engine-based generator work?
Post by: Geezer on 17/10/2011 00:12:06
Nice annimation! It's not clear to me what all the bits do. I understand the pontoon rising and falling in the tide, but I don't understand what the other tank thing is doing. Maybe a bit of a description might help?

BTW, assuming the energy is derived from the rise and fall of the pontoon, have you worked out a size to power ratio? Something along the lines of kilowatts per cubic meter or 1000 kg of displacement might be helpful. I think you should be able to get a good idea of it from the mass of water displaced by the pontoon, and the distance it moves in time.
Title: Re: Will this buoyancy engine-based generator work?
Post by: RD on 17/10/2011 01:03:55
Please let me have any comments (good or bad,) relating to my Buoyancy Engine idea

 [ Invalid Attachment ]

What is preventing horizontal and rotary motion by the “storage vessel" and “pontoon" due to ocean currents, causing the cables to become twisted/tangled which would prevention operation ?.

If the answer is “they are enclosed in an almost watertight lift-shaft built on the seabed” that’s gonna cost a fortune to construct to a standard which will survive being in the ocean.

BTW I suspect it would only be a matter of time before marine fouling would clog-up the pulleys.
Title: Re: Will this buoyancy engine-based generator work?
Post by: Geezer on 17/10/2011 02:39:29
I couldn't resist trying to work out the power.

Let's say the pontoon displaces 1000 metric tonnes and it moves 2 meters up and 2 meters down every 12 hours.

The force produced by the pontoon is 9.81*1000 = 9810 kN (kilo-newtons)

The average speed of the pontoon is 8/60/60 = 0.0022 m/s

Power is force times distance in time, so the average power (assuming the device produces power in both directions) is

0.0022*9810 = 21.6 kW (before you account for any parasitic losses)

(Did I get that right?)
Title: Re: Will this buoyancy engine-based generator work?
Post by: Geezer on 17/10/2011 03:56:40
(Did I get that right?)

No, I didn't!

I mucked up the speed. It should be 8/24/60/60 = 0.000093 m/s (93 micrcometers per second)

The average power would be 0.9 kW, so, if you are lucky, you might get about 1kW for every 1000t displacement. If I have that right, it means a very large supertanker could generate about 500kW.
Title: Re: Will this buoyancy engine-based generator work?
Post by: Geezer on 17/10/2011 07:30:12
Mootle,

I looked your idea and wondered if you have thought of using another method that might use compressed air instead of the cables and pontoons.

Imagine you have a (very large) thing like a diving bell that is anchored to the sea floor. The top of the bell does not need to be far below sea level. It just needs to be low enough that it remains fully submerged at the lowest tide.

There is a (very big) hose connected to the top of the bell. At low tide, we force air into the bell to dispel all the water from the bell. We then disconnect the compressor and seal the hose. The only thing that remains attached to the hose is a pressure gauge.

As the tide rises, the pressure in the hose will also rise as water is forced into the bell by the increased head of water relative to the bell. As the tide falls, the opposite happens.

The changing air pressure in the hose is a potential source of useful work. This may not be the most elegant way of tapping tidal energy, but in certain situations it might overcome a lot of the problems associated with corrosion and marine fouling. Also, it can be very robust, is largely invisible, and it has no impact on the flow of water through estuaries and the like.

The downside is that you either need one gigantic bell, or an enormous number of smaller bells connected in parallel, which is probably the only way to do it. I think it would be best if they are made of reinforced concrete.

The slowly fluctuating compressed air could be made to do a lot of different things, but I think the best thing to do with it would be to use it to pump water into an elevated reservoir that could produce electric power from water driven turbines when required.


 
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 17/10/2011 19:34:48
It seems much simpler to hang a big heavy float in the sea and let it rise and fall with the tide. Tie a rope to it and then connect that rope to a pulley. Have the other end of the pulley connected to a spring (or a counterweight).
When the tide falls it pulls the rope and turns the pulley. When the tide falls the spring or counterweight pulls the rope and turns the pulley the other way.
With this system there is less rope, it's all above water (and so is everything else apart from some sort of frame to hold it in place.)
Your system looks unduly complicated. Why have 6 ropes + pulleys when you can just put a gearbox on the generator shaft?
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 17/10/2011 20:01:47
Nice annimation! It's not clear to me what all the bits do. I understand the pontoon rising and falling in the tide, but I don't understand what the other tank thing is doing. Maybe a bit of a description might help?

Thanks. The Storage Vessel is submerged to a desired depth toward the bottom of the ocean by virtue of the pulley system which connects it to the pontoon via a cable. In the animation I've shown a 6:1 gearing ratio so for the 2m tidal range the Storage Vessel with descend by 2 x 6 to give 12m. The pulley is ratchetted so multiple cycles can be used to achieve the desired depth. Once the desired depth is achieved a valve can be opened to allow an inrush of water to a turbine. The turbine is linked to a generator. The greater to depth and flow the greater the potential for power generation.

BTW, assuming the energy is derived from the rise and fall of the pontoon, have you worked out a size to power ratio? Something along the lines of kilowatts per cubic meter or 1000 kg of displacement might be helpful. I think you should be able to get a good idea of it from the mass of water displaced by the pontoon, and the distance it moves in time.

A turbine and generator rated at 1.99MW with a working head of 50m and a Storage Vessel volume of 67,000m3 would provide the following revenue:

RO @ £100/MWh   £434,637.01/yr
FIT @ 11p/kWh   £478,100.71/yr
Export @ 3p/kWh   £130,391.10/yr
         £1,043,128.82/yr
   
£20,862,576.34/20yr based on 25:1 gearing or £208,625,763.39/20yr for 10 systems based on simple scaling.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 17/10/2011 20:46:36
Ah, but if the storage vessel is 67,000m3, the pontoon will have to displace six times that volume, or about 400,000 cubic meters, otherwise it will sink. A cubic meter of water weighs about 1t, so your pontoon displacement is about 400,000t which is about 80% of the supertanker I mentioned, and that is only capable of generating 0.5MW, so you are only going to get 0.4MW, and that's without allowing for the inevitable losses in the system

It doesn't matter how you cut it, but ultimately, the thing that is doing the work is the tide lifting the mass of water displaced by the pontoon against gravity. If your calculation says that you are doing more work than that, you are trying to get something for nothing, which has never worked thus far.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 17/10/2011 22:31:25
Ah, but if the storage vessel is 67,000m3, the pontoon will have to displace six times that volume, or about 400,000 cubic meters, otherwise it will sink. A cubic meter of water weighs about 1t, so your pontoon displacement is about 400,000t which is about 80% of the supertanker I mentioned, and that is only capable of generating 0.5MW, so you are only going to get 0.4MW, and that's without allowing for the inevitable losses in the system

It doesn't matter how you cut it, but ultimately, the thing that is doing the work is the tide lifting the mass of water displaced by the pontoon against gravity. If your calculation says that you are doing more work than that, you are trying to get something for nothing, which has never worked thus far.

The power generation calculation depends on the depth and the size of the pipe. I've applied typical turbine and motor efficiency and calculated the energy loss due to pumping out. These are standard calculations which I'm happy to post if necessary or you could post your calculation for review so I can see where I've managed to lose you?

Think of the idea as a portable dam. With a working head of 50m a much higher power output can be achieved by opting for a larger pipe or choosing a greater working head for the generation phase. There is always downside though and this idea is no exception, i.e., the storage tank would fill much faster and a higher rated turbine / generator set would cost more. This would only be worth investing in if the selling price of high instantaneous electricity upon demand was valued higher than a lower base load provision. At the moment the feed in tariff and renewable obligation are geared toward providing a base load provision. The pontoon sizing is another example where we can't get something for nothing, i.e., the greater the gearing ratio the greater the volume of the pontoon will need to be for a given storage vessel. The optimum gearing ratio for a 50m depth and 2m range would be 25:1. At this size we would need to make full use of the pontoon. Using it as a low cost platform for wind turbines or solar PV would be an obvious way to improve the return on investment. 
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 18/10/2011 03:29:55

The power generation calculation depends on the depth and the size of the pipe.


Alas, it does not. To generate power you need to do work, and the only thing that's doing any work is the tide elevating the pontoon against the force exerted by the cable. It's quite simple to determine how much work the tide does, or the power, which is the rate of doing work. I calculated that in my previous posts.

You can do anything you like with systems of gears and cables, but you will never be able to use them to multiply the amount of work done by the tide acting on the pontoon. The second law of thermodynamics has yet to be broken.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 18/10/2011 10:26:55
seems to me that Geezer is correct (damn) - I will note also that 400k metric tonnes deadweight (available displacement for cargo - or in your case provide buoyancy force) is bigger than all but a dozen or ships in the world today.  Large cargo ships (no one says supertankers apart from the press) are not designed to be pulled from underneath by cables but to have cargo spread evenly over about 15000m2 of bottom.  For your guidance - to construct a tanker of 400k dwt you use about us$25-30million worth of steel
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 18/10/2011 17:19:15
seems to me that Geezer is correct (damn) -

Actually, he's not! I cocked up the distance by counting both the rising and falling distance. That's not right; work is only done on the pontoon when the tide is rising. I overestimated the power by a factor of two.

A half million tonne pontoon can only generate 250kW (average) which, coincidentally, is the same as the maximum power output of the engine in my truck  [:D] 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 18/10/2011 19:46:30

The power generation calculation depends on the depth and the size of the pipe.


Alas, it does not. To generate power you need to do work, and the only thing that's doing any work is the tide elevating the pontoon against the force exerted by the cable. It's quite simple to determine how much work the tide does, or the power, which is the rate of doing work. I calculated that in my previous posts.

You can do anything you like with systems of gears and cables, but you will never be able to use them to multiply the amount of work done by the tide acting on the pontoon. The second law of thermodynamics has yet to be broken.

I offered to review your calculations or show you the calculations I've used. You've chosen a third option. Unfortunately, your way takes the debate no further forward and denies us a learning opportunity, where either you learn something new or I do.

However, strongly you assert something it means nothing without proof!
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 18/10/2011 20:07:10
What is preventing horizontal and rotary motion by the “storage vessel" and “pontoon" due to ocean currents, causing the cables to become twisted/tangled which would prevention operation ?.

Hi, thanks for your feedback. The schematic animation is a little misleading, it is more clear in the scaled model that I'm developing. However, I will try to describe in words. The Storage Vessel would be shaped like a submarine. The Pontoon would be shaped such that the Storage Vessel rises up into a hollowed out centre (a bit like an oval shaped polo mint). The Pontoon would include various overhead gantries spanning the hollowed centre (shortways,) each with a pair of compound pulleys. Each set of cables would pass through guides mounted onto the outer shell of the Storage Vessel. The cables would be highly tensioned at all times. I would anticipate that this would be sufficient To minimise drift but I would agree that some simulation modelling will be needed to verify the effects and account for variability. The storage vessel would be turned into any prevailing current but ordinarily the site would be selected to avoid strong current systems.

If the answer is “they are enclosed in an almost watertight lift-shaft built on the seabed” that’s gonna cost a fortune to construct to a standard which will survive being in the ocean.

Again, I can see why you might get that impression. The idea is intended for the open ocean. I had to place the animation in a box to avoid strange effects in the video as it rescaled with the movement of the tide.

BTW I suspect it would only be a matter of time before marine fouling would clog-up the pulleys.

This is a real engineering challenge but I'm sure it's not a new problem. I would seek consultation with marine engineers but anticipate a few practical mitigation's as follows;

1. Keep things moving.
2. Select large diameter pulleys.
3. Don't compromise on material selections.
4. Fit scraping devices.
5. Include planned maintenance tasks.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 18/10/2011 21:00:26
OK, let's have another look at the maths.
"A turbine and generator  with a working head of 50m and a Storage Vessel volume of 67,000m3 would provide the "

In the right units, pressure times volume = energy
50m of depth in water with a density of 1000 kg/m^3 will exert a pressure of
(rho) g h =
1000 X 10 * 50 =500,000 pascal (that's about right: it's 5 bar which is what you would expect with 10m head of water being about 1 bar)
The volume is 67000 so the stored energy is
500,000*67,000
33.5 GJ
That sounds good, but it's only roughly the energy stored in 1000 litres of cooking oil or gasoline.
That energy is available twice a day so that's once every 12 hour
720 minutes
43200 seconds
So the power is 33,500,000,000 /43,200 which gives you
0.78MW average power. That's not a lot.

To do that you would need 67000 tons moving up and down by 50 metres or roughly 500,000 tons moving up and down 8.3 metres.

But it only moves by about 4 metres so the energy is only half what I calculated.
So the power output is about 400KW for a roughly supertanker sized pontoon.
That's the same ballpark as Geezer's figure. (Possibly the reason it's bigger is because I haven't included the energy needed to blow the tank clear each time)

Do you have any real evidence that the output will be better?
If not, perhaps you would do better to study some thermodynamics rather than say things like "However, strongly you assert something it means nothing without proof!"


Incidentally, you might like to answer the questions I asked earlier.
"Why have 6 ropes + pulleys when you can just put a gearbox on the generator shaft?"
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 18/10/2011 22:10:41
seems to me that Geezer is correct (damn) - I will note also that 400k metric tonnes deadweight (available displacement for cargo - or in your case provide buoyancy force) is bigger than all but a dozen or ships in the world today.  Large cargo ships (no one says supertankers apart from the press) are not designed to be pulled from underneath by cables but to have cargo spread evenly over about 15000m2 of bottom.  For your guidance - to construct a tanker of 400k dwt you use about us$25-30million worth of steel

Thanks for this. Accurate costing information is vitally important and I would be most grateful if you can provide any source information on this. I'm second guessing that the Pontoon sizing that has been used above is a false assumption carried forward from the schematic animation. As stated, the scaled animation is based on a 25:1 gearing ratio and would thus require a larger pontoon.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 18/10/2011 22:49:19
OK, let's have another look at the maths.
"A turbine and generator  with a working head of 50m and a Storage Vessel volume of 67,000m3 would provide the "

In the right units, pressure times volume = energy
50m of depth in water with a density of 1000 kg/m^3 will exert a pressure of
(rho) g h =
1000 X 10 * 50 =500,000 pascal (that's about right: it's 5 bar which is what you would expect with 10m head of water being about 1 bar)
The volume is 67000 so the stored energy is
500,000*67,000
33.5 GJ
That sounds good, but it's only roughly the energy stored in 1000 litres of cooking oil or gasoline.
That energy is available twice a day so that's once every 12 hour
720 minutes
43200 seconds
So the power is 33,500,000,000 /43,200 which gives you
0.78MW average power. That's not a lot.

To do that you would need 67000 tons moving up and down by 50 metres or roughly 500,000 tons moving up and down 8.3 metres.

But it only moves by about 4 metres so the energy is only half what I calculated.
So the power output is about 400KW for a roughly supertanker sized pontoon.
That's the same ballpark as Geezer's figure. (Possibly the reason it's bigger is because I haven't included the energy needed to blow the tank clear each time)

Do you have any real evidence that the output will be better?
If not, perhaps you would do better to study some thermodynamics rather than say things like "However, strongly you assert something it means nothing without proof!"

Hi, thanks for this, happy to show how I've come to my generator rating. fyi I have studied thermodynamics during my Masters in BSE & Sustainable Energy but I didn't mean anything by the comment other than trying to get to the bottom of the descrepancy. If I'm wrong I want to know why and I cannot do that without knowing how the figures are reached but I've suggested a possible reason in my previous email.

The equation used for generation and pumping is the same:

Pgen = (gen eff*rLLw*g*dLL*Agen*(2*9.81*dLL)^0.5)/1000000
2MW = (0.85 * 1,025 * 9.81 * 50 *0.15 * (2 * 9.81 * 50)^0.5)/1000000
Where
gen eff, generator efficiency = 85%
rLLw, ocean density at depth = 1025kg/m3
g, gravity = 9.81m/s2
dLL, depth at LL = 50m
Agen, Gen Supply Pipe Area = 0.15m2

Following your calculation I think the issue is one of time. The difference seems to be in the time frame applied. For the optimum operation, i.e., generation would only be possible for a shorter amount of time than the 12hr period indicated.

Incidentally, you might like to answer the questions I asked earlier.
"Why have 6 ropes + pulleys when you can just put a gearbox on the generator shaft?"

I hadn't considered the gearbox idea and can see a number of benefits which are well worth exploring. Thank you.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 18/10/2011 22:57:31

The power generation calculation depends on the depth and the size of the pipe.


Alas, it does not. To generate power you need to do work, and the only thing that's doing any work is the tide elevating the pontoon against the force exerted by the cable. It's quite simple to determine how much work the tide does, or the power, which is the rate of doing work. I calculated that in my previous posts.

You can do anything you like with systems of gears and cables, but you will never be able to use them to multiply the amount of work done by the tide acting on the pontoon. The second law of thermodynamics has yet to be broken.

I offered to review your calculations or show you the calculations I've used. You've chosen a third option. Unfortunately, your way takes the debate no further forward and denies us a learning opportunity, where either you learn something new or I do.

However, strongly you assert something it means nothing without proof!

Apparently you didn't like my calculations  [:D]

OK, here we go again, from the top!

To generate power something has to do work. We are trying to derive power from tidal energy, so it must be the tide that's doing the work - so far so good, (I hope).

According to Wikipedia (Work) - "The SI unit of work is the joule (J), which is defined as the work done by a force of one newton acting over a distance of one meter."

In this case it's the vertical pull on the cable caused by the pontoon rising in the tide that is doing all the work (if you don't believe me, please tell me what other source of energy you are tapping into.)

So, if we know how far the pontoon was raised by the tide and the force exerted by the cable, we can multiply one by the other to determine the amount of work done (in joules).

The force in the cable equals the force produced by the buoyancy of the pontoon acting against gravity, which is 9.81 times the mass of water displaced - (don't blame me, blame Archimedes.)

If the pontoon displaces 400,000t or 400,000,000kg (which it must in order to submerge a 67,000 cubic meter storage vessel with a 6:1 mechanical ratio) the force in the cable is 9.81 times 400,000,000 = 3,924,000,000N. (Could be quite a thick cable!)

We know the tide lifts the pontoon 2 meters twice a day, or 4 meters in 24 hours.

Therefore, the work done per day (force times distance) is 9.81 x 400,000,000 x 4 = 15,700 MJ (megajoules)
The average work done in one second must be that value divided by 86,400.

Therefore, average work per second is 15,700,000,000/86,400 = 182,000 J/s = 182kJ/s

A watt is a rate of doing work at 1 J/s (joules per second), so the average power is 182kW. It looks to me that you are assuming continuous generation in your calculations, in which case you better be using average power, not peak power.

BTW, 1 megawatt-hour equals 3,600 MJ (megajoules), so 15,700 MJ per day can generate a maximum of 4.36 MWh per day.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 18/10/2011 23:05:42
Apparently you didn't like my calculations  [:D]

OK, here we go again, from the top!

Thanks for this. I think our last posts crossed in the ether but my last post identifies the descrepancy as the generation time. There would not be a full 12hrs available to generate. I have allowed a smaller amount of time, i.e., your equation would balance.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 19/10/2011 00:17:54
I was thinking you might consider something like this -

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 [ Invalid Attachment ]


Also available as a PDF - see link at end of message.

It's basically a concrete tank that's open to the sea near the bottom. Compressed gas displaces the water in the tank. The rising tide increases the pressure. It probably needs to be an inert gas that won't dissolve in water. Nitrogen perhaps - BC?

At the other end of the pipe, and it could be a long distance away, is a similar arrangement only with different dimensions, that elevates fresh water into a storage reservoir. What you end up with is a pumped storage hydroelectric generator that uses tidal energy to pump the water up to the storage reservoir.

Doing work with compressed gas is usually horribly inefficient, but that may not be the case here because the rate of compression is very slow. So slow in fact, that the pressure in the pipe would be constant if the work taken out at the pump end was the same as the work put in by the tide. There is no change in the energy stored in the gas if the pipe is sized properly.

It's a very sketchy idea, and there are probably a whole bunch of nasty issues, but it might be reasonably compatible with a harsh marine environment. I've no idea how the economics would work out, but I do know you would need an awful lot of tanks to generate a significant amount of power. On the other hand, it might be a lot more acceptable than a bunch of whopping great wind turbines growing out of the sea.

(The pipe does not need to stick up above sea level as shown - it could be routed along the seabed. The entire caboodle would obviously have to be anchored to the seabed with number 9 screws to stop it floating away!)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 20/10/2011 10:19:08
I would need to see the whole system to be able to offer a more meaningful comment.

With a static system the output would be greatly diminished. There is the potential to employ the storage element to generate a useful and reliable power output when the demand is there, which is a common failing of other renewables. The real challenge is to get an investor a return on investment.

My preference is to use a dynamic system working with water rather than a static system working with compressed air as denser working fluid and greater pressure differential gives a better energy density and output capability.

btw please confirm if you now concede the point on capacity?
Title: Will this buoyancy engine-based generator work?
Post by: peppercorn on 20/10/2011 11:57:55
Mootle,

I looked your idea and wondered if you have thought of using another method that might use compressed air instead of the cables and pontoons.

We done dis idea before dint we [:P]

Here:
How much work in the form of pressure is there at the bottom of the deep ocean? (http://www.thenakedscientists.com/forum/index.php?topic=31433)

... oh, and here:
Does deep ocean have potential energy due to pressure? (http://www.thenakedscientists.com/forum/index.php?topic=36659)
 [:-X]
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 20/10/2011 17:47:03
Whilst some of the concepts are similar to some earlier threads here I would venture that there are several key differences to the animimation which is linked to in the original post. My idea is patent pending so I guess I'll know if the idea has been done before if the IPO decide to grant the patent or not. However, according to searches to date it is a new arrangement.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 20/10/2011 18:00:38
btw please confirm if you now concede the point on capacity?


What point? Are you saying your system will be able to produce more than 4.36 MWh per day?

If you believe that is the case, please take a look at this informative video
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 20/10/2011 18:39:39
We done dis idea before dint we [:P]

Here:
How much work in the form of pressure is there at the bottom of the deep ocean? (http://www.thenakedscientists.com/forum/index.php?topic=31433)

... oh, and here:
Does deep ocean have potential energy due to pressure? (http://www.thenakedscientists.com/forum/index.php?topic=36659)
 [:-X]

I think those were more to do with energy storage. The subsea pressure tank thing is just a way of tapping tidal energy. While the air in the tank is being forced out of the tank by the rising tide, it would drive a pump to elevate fresh water into a high level reservoir for subsequent use by a water turbine.

The tank would have to be enormous to pump a lot of water, or there would have to be a lot of them, and the static head between the high and low fresh water reservoirs would determine how much water could be elevated. However, the turbine would still extract the same amount of work. A greater head just means a smaller turbine can do the same amount of work (assuming they are equally efficient).

The amount of water displaced by the tide in the air tank determines the amount of work that the system can do. In that respect it is no different from a pontoon doing work by rising on the tide and pulling on a cable.

The advantage of the compressed air approach is that there are no moving parts immersed in salt water, and there is nothing to get kicked around by currents and storms. It's a concrete box, so it should last quite a long time with zero maintenance. The pipe to bring the air ashore would be a weaker point. Mind you, if the system was designed so that the pump was driven very slowly as the tide came in (constant air pressure driving a whopping great piston) the pipe bore would be really small compared to the size of the tank.

BTW, if somebody didn't already patent this idea, it's too late now [:D] 
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 20/10/2011 19:10:14
The patent office are quite happy to take your money without checking (or caring) if the idea works.
I still think this idea is pointless. It needs a really big construction project to make relatively little power.
Fundamentally it  can not extract more energy from the tide than my suggestion of a big box on a rope. The only aspect of it that might be novel enough to get a patent is the use of the rope and pulleys to convert a small movement with a large force into a larger movement with a smaller force. Obviously, that's been done before but probably not in this context because it doesn't offer any great advantage.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 20/10/2011 20:37:50

The patent office are quite happy to take your money without checking (or caring) if the idea works.


Yup, that about sums it up. Their initial response is usually to reject everything you claim so they can stick your application back at the bottom of the heap [:)]
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/10/2011 09:37:28
Ah, but if the storage vessel is 67,000m3, the pontoon will have to displace six times that volume, or about 400,000 cubic meters, otherwise it will sink. A cubic meter of water weighs about 1t, so your pontoon displacement is about 400,000t which is about 80% of the supertanker I mentioned, and that is only capable of generating 0.5MW, so you are only going to get 0.4MW, and that's without allowing for the inevitable losses in the system

It doesn't matter how you cut it, but ultimately, the thing that is doing the work is the tide lifting the mass of water displaced by the pontoon against gravity. If your calculation says that you are doing more work than that, you are trying to get something for nothing, which has never worked thus far.

Geezer - does it help if I remind you of the point to which I was referring (see above). The total energy available is not the generation rating. However, the total energy available was given as part of the build up to the revenue calculation.

To repeat, do you now concede that the rating claim was in fact ok.   
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/10/2011 10:05:53
The patent office are quite happy to take your money without checking (or caring) if the idea works.
I still think this idea is pointless. It needs a really big construction project to make relatively little power.
Fundamentally it  can not extract more energy from the tide than my suggestion of a big box on a rope. The only aspect of it that might be novel enough to get a patent is the use of the rope and pulleys to convert a small movement with a large force into a larger movement with a smaller force. Obviously, that's been done before but probably not in this context because it doesn't offer any great advantage.

I'm not sure I agree with your comments regarding the IPO, at least this hasn't been my experience.

Renewables (including tidal) is a very active research area. The reason for this is that various government incentives are in place to make investment into new developments more viable. I would have to agree that without the incentives, investment would not be possible but now they are new possibilities come to light - 'necessity is the mother of all invention'. I tend to think in terms of jobs for the people of the UK and would regard large engineering projects such as this, a good thing for social mobility provide there is a good rate of return. Like it or not we face an extreme energy shortage which is set to get worse. I doubt a quick fix will come along, so we need to get our thinking caps on now and plan for the future. Otherwise, what will happen when the gas, coal and uranium becomes uneconomical to extract? It's easy to forget that gas, coal and nuclear were massive infrastructure projects.

A big advantage of this system is that the rating of the system can be geared / scaled to suit the demand and unlike wind and solar would be completely reliable. The UK's energy demand profile isn't smooth, it has peaks and troughs and the system will fall over if the peaks can't be met. If the UK is to meet its commitments on renewables we will need a well thought out mix of technologies, get that mix wrong and there is a very real risk that the lights will go out in the not so distant future.

At the moment we get by with help from our French compatriots but as population increases and power infrastructure capacity declines, when push comes to shove we must be self reliant or face severe penalties when we have to tell industry to turn off their manufacturing plants.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/10/2011 10:21:06
btw please confirm if you now concede the point on capacity?


What point? Are you saying your system will be able to produce more than 4.36 MWh per day?

If you believe that is the case, please take a look at this informative video

fyi, each of the buoyancy engines would provide ca. 12MWh/day, giving a total of around 120MWh/day for the set of (10) described in the revenue calculation given previously. This is a nett figure including purge pumping and ancillary losses but I suspect the discrepancy is in the gearing ratio which has been applied.

As for the video - I did like that  [:D]
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 21/10/2011 17:59:59

fyi, each of the buoyancy engines would provide ca. 12MWh/day,


Then you are trying to violate the second law of thermodynamics. It's not up for "debate". It's really quite simple. You cannot extract more work from a system than the work that was put into the system. The tide is the thing that is putting in the work, but you seem determined to ignore that inconvenient fact.

My calculation clearly shows each generator can't possibly produce more than 4.36MWh per day (and it will actually be a lot less due to parasitic losses.) If there is a flaw in my calculation, you should be able point it out, quite easily. Either you don't understand basic science, or you didn't make any attempt to understand what I posted.

I'm not going to waste any more time trying to help you understand where you are going wrong, and please don't blame me if you are chased out of town by an angry mob of investors who want their money back. (You won't be able to blame the patent office either.)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/10/2011 11:56:00
Then you are trying to violate the second law of thermodynamics. It's not up for "debate". It's really quite simple. You cannot extract more work from a system than the work that was put into the system. The tide is the thing that is putting in the work, but you seem determined to ignore that inconvenient fact.

I'm not trying to ignore anything but rather get you to acknowledge that a simple misunderstanding has caused the discrepancy.

My calculation clearly shows each generator can't possibly produce more than 4.36MWh per day (and it will actually be a lot less due to parasitic losses.) If there is a flaw in my calculation, you should be able point it out, quite easily. Either you don't understand basic science, or you didn't make any attempt to understand what I posted.

If anyone is not following the thread it's you. I have shown my rating calculation and identified why there is a discrepancy: 1, You assumed a longer generation time than me (I've allowed for the Storage Vessel ascent time,) 2, You assumed the 6:1 gearing ratio of the schematic animation would carry forward when it was stated that the gearing ratio of the Scaled application is 25:1 which in turn increases the Pontoon volume.

I'm not going to waste any more time trying to help you understand where you are going wrong, and please don't blame me if you are chased out of town by an angry mob of investors who want their money back. (You won't be able to blame the patent office either.)

There are a few issues here, 1, you've made various errors throughout this thread and it's difficult to see how you've reached the conclusion that I don't understand the principles involved. 2, In fairness you've acknowledged some of your errors but you seem to have a major issue conceding the point of the rating which comes about from your mishandling of total energy vs energy flow. 3, I'm not looking to blame anyone for anything - I have no idea where you get that from. 4. As for the total energy available, if you substitute the correct Pontoon volume and density based on the 25:1 gearing ratio which I gave then you will understand why it is your input to the calculation that is flawed.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 22/10/2011 16:47:06
The patent office are quite happy to take your money without checking (or caring) if the idea works.
I still think this idea is pointless. It needs a really big construction project to make relatively little power.
Fundamentally it  can not extract more energy from the tide than my suggestion of a big box on a rope. The only aspect of it that might be novel enough to get a patent is the use of the rope and pulleys to convert a small movement with a large force into a larger movement with a smaller force. Obviously, that's been done before but probably not in this context because it doesn't offer any great advantage.

I'm not sure I agree with your comments regarding the IPO, at least this hasn't been my experience.



I only made one comment about the patent office. That comment is that they do not check if things work.
Do you think they have the time or facilities to test all the inventions they are asked about?


Also, in your debate with Geezer you seem not to have understood where the discrepancy is.
The fundamental difference is between what you are claiming and what the laws of physics will allow.
If your ideas do not tally with reality then it is not reality that has got it wrong.

Incidentally, there is one aspect of inventions that the PO looks at before awarding a patent. They don't patent perpetual motion machines.
If you were to connect the output of your system to a pump to make an "artificial tide" then you would have made a perpetual motion machine. They certainly wouldn't patent that.

Your system might provide a possible benefit in places where the tidal range is too small to use conventionally, but even there it would be pointless because there simply would not be enough energy available to make it worth while.

Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/10/2011 17:43:37
I only made one comment about the patent office. That comment is that they do not check if things work.
Do you think they have the time or facilities to test all the inventions they are asked about?

I agree, it is not the job of the patent office to check if things work or not. But that wasn't the point I objected to it was the comment about them not caring.

Also, in your debate with Geezer you seem not to have understood where the discrepancy is.
The fundamental difference is between what you are claiming and what the laws of physics will allow.
If your ideas do not tally with reality then it is not reality that has got it wrong.

The 'reality' is that Geezer put the wrong figures into the calculation - a point that I've made several times. If anything, I find it amusing that people who obviously have an understanding of the principles cannot concede a point when the error has been clearly identified. The point would have been easy to concede since it is easy to see where the misunderstanding arose. However, to maintain the position after the corrections given is dissapointing. I asserted a nett energy of 12MWh/day. If we compare this with the calculation you kindly indicated earlier and account for the cycle occurring twice per day we have a gross energy available of 500,000 * 67,000 * 2 = 67GJ or 18.6MWh/day. The difference being my allowance for purge pumping and ancillary motor drives, i.e., the equation balances.

Incidentally, there is one aspect of inventions that the PO looks at before awarding a patent. They don't patent perpetual motion machines.
If you were to connect the output of your system to a pump to make an "artificial tide" then you would have made a perpetual motion machine. They certainly wouldn't patent that.

You will be aware that there are several types of perpetual motion. This idea is powered by the gravitation forces of the planets, the sun and the moon. Perpetual motion is not one of the claims of my patent application. This is what causes the tide and so this would not be a perpetual motion machine of the 1st kind - to which you refer. It is true that as the tides persist the machine could continue to function, providing it is properly managed. In this respect, it is no different to a solar PV system / battery powering a motor continuously. If your 'system' boundary did not extend to the sun, you might draw the conclusion that this is also a violation of the laws of thermodynamics but I think you will find such systems have been granted patents. The total energy to lift the 'correct' sized Pontoon does not exceed the power generated - if Geezer reran his calculations he would see that.

Your system might provide a possible benefit in places where the tidal range is too small to use conventionally, but even there it would be pointless because there simply would not be enough energy available to make it worth while.

The system has the potential to exceed the power output of conventional tidal systems. In the scaled model (10) 2MW buoyancy engines would be able to reliably power 14,500 smaller homes or 9,000 average sized homes. The viability, rests with the return on investment. I won't know if this stacks up until I've completed the scaled model and assessed the costings.

This thread has become scrambled by misunderstanding part of which I'm to blame. The schematic animation was only intended to show the basic operation, so I think I'll bow out at this point and work on presenting the idea in a more coherent way. Once, I've completed the scaled animation I would like to pick up, if that's OK?

Thanks to 'everyone' for their input, it was informative especially the possible gearing adaptation and costing information - much appreciated!
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/10/2011 21:15:07
I asserted a nett energy of 12MWh/day.

You can assert as often or as loudly as you care to, but according to the data you provided, it remains impossible to exceed 4.36mWh per day [;D]

If it's so obvious to you that I mucked up the calculation I used to determine that figure, you might want to point out where I went wrong.

Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 23/10/2011 09:52:35
I asserted a nett energy of 12MWh/day.

You can assert as often or as loudly as you care to, but according to the data you provided, it remains impossible to exceed 4.36mWh per day [;D]

If it's so obvious to you that I mucked up the calculation I used to determine that figure, you might want to point out where I went wrong.

I have, more than once, but to my frustration you've not conceded the point on rating nor have you followed the instruction and input the correct Pontoon volume into your energy calculation based on the 25:1 (rather than the 6:1, used for demonstration purpose of the ratchet pulley system in the schematic animation) gearing ratio.

Further, I've modified Bored chemist's calculation as a check to take into account the twice daily operation and this verifies that my asserted energy balance is ok.

From your comments, I can see where you've got the wrong end of the stick so in this regard I'm afraid that I've failed to properly convey the full operation of the system but this is something I plan to put right with the scaled animation.

Once again, thank you for your input.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 23/10/2011 15:13:10
I asserted a nett energy of 12MWh/day.

You can assert as often or as loudly as you care to, but according to the data you provided, it remains impossible to exceed 4.36mWh per day [;D]

If it's so obvious to you that I mucked up the calculation I used to determine that figure, you might want to point out where I went wrong.

I have, more than once, but to my frustration you've not conceded the point on rating nor have you followed the instruction and input the correct Pontoon volume into your energy calculation based on the 25:1 (rather than the 6:1, used for demonstration purpose of the ratchet pulley system in the schematic animation) gearing ratio.

Further, I've modified Bored chemist's calculation as a check to take into account the twice daily operation and this verifies that my asserted energy balance is ok.

From your comments, I can see where you've got the wrong end of the stick so in this regard I'm afraid that I've failed to properly convey the full operation of the system but this is something I plan to put right with the scaled animation.

Once again, thank you for your input.

No wonder you keep getting the wrong answer.
I already allowed for the fact that the tide rises twice a day. that's why my post includes this "That energy is available twice a day so that's once every 12 hour"
So, if you don't change my maths to make it wrong, it pretty much tallies with Geezer's.

Rather than repeatedly saying that you have pointed out his error (which, as far as I can see, you have not) could you please point it out now?

If it doesn't work with a 6 to one ratio, it also won't work with 25 to one. You don't get more energy out than the tide puts in, no matter how much rope you use.

I ask you to calculate how much energy you would need to use (with an idealised, perfect crane) to raise the pontoon, rather than using the tide.
If it turns out to be less than 12MW Hr a day then you don't need the tide at all.
You have then made a perpetual motion machine that doesn't rely on the moon.
Your proposal breaches that principle of conservation of energy.
It's that sort of perpetual motion machine, and the PO won't patent it. (And if they cared they would check- they don't have time or kit to do either)

When it comes down to it, for the cost of a supertanker sized building project (and then some for the other structures) you can get a bit less than 0.4MW
You say that electricity is £100 per MW Hr, fair enough.
0.4MW for 24Hr gives £960 per day in revenue. Call it £1000 to make the maths easy
The money markets are screwed at the moment so let's assume you can borrow money at 2% (which is ridiculously cheap)
1000 a day is £365000 per year which will cover a debt (interest only without paying capital) of £18M
But the steel alone will cost you £15M
That leaves no room for any of the generator, the concrete to hold it in pace, paying off the capital, designing, building and so on.

Your idea doesn't make sense.
With a more realistic interest rate, like 5%, it still makes no sense, even if we ignore the laws of physics and let you get out twice as much energy as the ocean puts in.

Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 23/10/2011 16:54:55
No wonder you keep getting the wrong answer.
I already allowed for the fact that the tide rises twice a day. that's why my post includes this "That energy is available twice a day so that's once every 12 hour"
So, if you don't change my maths to make it wrong, it pretty much tallies with Geezer's.

The error is that neither of you seem understand how the Buoyancy Engine works.

The reason for the modification to your maths is that the Storage Vessel descends twice per day but each time ascends to the surface due to its own buoyancy (since it remains buoyant even when full of water).

Therefore, the energy is 500,000 * 67,000 * 2 = 67GJ (check) rather than the 33.5GJ that you have indicated.

Rather than repeatedly saying that you have pointed out his error (which, as far as I can see, you have not) could you please point it out now?

If it doesn't work with a 6 to one ratio, it also won't work with 25 to one. You don't get more energy out than the tide puts in, no matter how much rope you use.

Your calculation is based on the working head and the Storage Vessel volume this checks out with the generator calculation I provided that is also based on the working head and the Storage Vessel volume.

For the Pontoon we can do the check sum by finding the mass (displaced) for 67,000 * 25 = 1,675,000m3
(the gearing ratio makes all the difference since this drives the required storage vessel).

Using sea water @ a density of 1,025kg/m3 this gives a mass of 1,716,875,000kg

1,716,875,000 * 4 * 9.81 = 67GJ (check)

I ask you to calculate how much energy you would need to use (with an idealised, perfect crane) to raise the pontoon, rather than using the tide.
If it turns out to be less than 12MW Hr a day then you don't need the tide at all.
You have then made a perpetual motion machine that doesn't rely on the moon.
Your proposal breaches that principle of conservation of energy.
It's that sort of perpetual motion machine, and the PO won't patent it. (And if they cared they would check- they don't have time or kit to do either)

I think we're getting into a bit of a circuitous argument here. If you wish to do more maths even though the calculation checks out all ways then please be my guest.

When it comes down to it, for the cost of a supertanker sized building project (and then some for the other structures) you can get a bit less than 0.4MW

The power rating could be any number of values depending on the desired fill time of the Storage Vessel, I've chosen one that fits with the optimum cycle time to get the most out of the Feed in Tariff. Much greater power outputs could be achieved but the fill time would be faster. Alternatively, if a location can be found where the ocean depth affords a greater working head whilst maintaining the tidal range, there is also scope for scaling up.

You say that electricity is £100 per MW Hr, fair enough.

No this is the revenue due the Renewable Obligation certificates. Electricity Export and Feed in Tariff is given separately.

0.4MW for 24Hr gives £960 per day in revenue. Call it £1000 to make the maths easy
The money markets are screwed at the moment so let's assume you can borrow money at 2% (which is ridiculously cheap)
1000 a day is £365000 per year which will cover a debt (interest only without paying capital) of £18M
But the steel alone will cost you £15M
That leaves no room for any of the generator, the concrete to hold it in pace, paying off the capital, designing, building and so on.

We obviously disagree about the fundamental output of the system and you have disregarded the revenue information given previously which somewhat alters the financial viability. However, I do intend to obtain meaningful costings in the fullness of time. However, wrt the interest rates this is accounted for since the government incentives are index linked over 20yrs.

Your idea doesn't make sense.
With a more realistic interest rate, like 5%, it still makes no sense, even if we ignore the laws of physics and let you get out twice as much energy as the ocean puts in.

I think your conclusions are premature and flawed but nevertheless I thank you for your input.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 23/10/2011 18:09:02
I understand perfectly well how it works, and I also understand that you have magically made the pontoon more than four time larger to let you reverse into your original, incorrect, power calculation.

The pontoon is now 3.5 times larger than the World's biggest supertanker (er, or whatever Matt wants us to call it.)

This isn't the Tommmy Cooper Show ewe know  [;D]

"The 'reality' is that Mootle put the wrong figures into the calculation - a point that I've made several times. If anything, I find it amusing that people who obviously have an understanding of the principles cannot concede a point when the error has been clearly identified."
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 23/10/2011 18:37:23
I understand perfectly well how it works, and I also understand that you have magically made the pontoon more than four time larger to let you reverse into your original, incorrect, power calculation.

The pontoon is now 3.5 times larger than the World's biggest supertanker (er, or whatever Matt wants us to call it.)

This isn't the Tommmy Cooper Show ewe know  [;D]

"The 'reality' is that Mootle put the wrong figures into the calculation - a point that I've made several times. If anything, I find it amusing that people who obviously have an understanding of the principles cannot concede a point when the error has been clearly identified."

So, do you now agree that when the correct volume figures are used for the Pontoon the energy calculation balances and that the power rating is also correct?

I find it hard to see how anyone following the thread would draw the conclusion that I have used the wrong figures since my calculation has not changed throughout. I cannot understand why you are reacting the way you are, as it is easy to see why the misunderstanding took place. However, I would once again apologise for my part in not making the schematic video as clear as it could have been.

Fyi, I have stated several times throughout the course of this thread that the schematic animation is to demonstrate the principle only. I'm working on the scaled animation and this thread has taught me the need to emphasis certain key aspects. Furthermore, the 25:1 gearing ratio is mentioned toward the end of the scaled animation and I also mention the 25:1 gearing ratio when setting out the revenue calculation for the scaled version, earlier in this thread.

Since you correctly identified that increasing the gearing would result in a larger Pontoon I did not feel the need to show all the intermediate steps, although in hindsight this would have been beneficial.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 23/10/2011 19:41:27
What I agree is that you never even bothered to look at what BC and I posted (despite repeated requests), because, if you had, you would have had ample opportunity to object to the numbers we were using.

If you were proposing a displacement of 1.7Gt, why didn't you simply point that out five or more days ago? Did I hide that information in my calculation? Was the pontoon displacement never discussed? In fact, up until now, you have not provided ANY value for the displacement of the pontoon, despite the fact that it is critical in determining the amount of work done. 

I don't suppose that's because you only just worked it out based on the information we gave you?

EDIT: Correction - that should be 1.7Mt (not 1.7Gt)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 23/10/2011 21:12:40
What I agree is that you never even bothered to look at what BC and I posted (despite repeated requests), because, if you had, you would have had ample opportunity to object to the numbers we were using.

If you were proposing a displacement of 1.7Gt, why didn't you simply point that out five or more days ago? Did I hide that information in my calculation? Was the pontoon displacement never discussed? In fact, up until now, you have not provided ANY value for the displacement of the pontoon, despite the fact that it is critical in determining the amount of work done. 

I don't suppose that's because you only just worked it out based on the information we gave you?

EDIT: Correction - that should be 1.7Mt (not 1.7Gt)


The truth of the matter is, those were your calculations and I pointed out (albeit indirectly,) that you had used incorrect values, stating that the figures balanced on several occasions in the knowledge that you could self-correct. I try to avoid redoing other peoples calculations, preferring to guide toward an answer - I find this more respectful. Having reviewed the thread I could have spelled things out to you in a more step by step way but in fairness I did make a real effort to reply fully to all the posts, even though some of yours came with a distinct sarcastic undertone.

Sadly, it looks as though you will never concede the points on capacity or total energy despite the evidence supporting this prognosis, preferring instead to making unsubstantiated speculation as to my understanding of my own idea despite ready acknowledgement of any contributions that I hadn't already considered.

I really don't understand why it is so hard for you to concede these points, nor why you are so quick to be disrespectful but eh oh - each to their own!
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 23/10/2011 22:23:18
Mootle, old bean, if you look back down the thread you will see I said this;

"If the pontoon displaces 400,000t or 400,000,000kg (which it must in order to submerge a 67,000 cubic meter storage vessel with a 6:1 mechanical ratio) the force in the cable is 9.81 times 400,000,000 = 3,924,000,000N."

I also asked you several times to point out any errors in my calculation.

Now you are saying you knew all along that I should have been using a displacement of more than four times that amount and a ratio of 25:1?

I really hope you didn't know that all along, because if you did, and you didn't bring it up, you were simply being a troll. I will give you the benefit of the doubt and assume that you had no idea what the displacement was until you recently figured it out.
Title: Will this buoyancy engine-based generator work?
Post by: Johann Mahne on 24/10/2011 04:33:33
Mootle,
What's the reason for not building a scale model?
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/10/2011 11:51:04
Mootle, old bean, if you look back down the thread you will see I said this;

"If the pontoon displaces 400,000t or 400,000,000kg (which it must in order to submerge a 67,000 cubic meter storage vessel with a 6:1 mechanical ratio) the force in the cable is 9.81 times 400,000,000 = 3,924,000,000N."

I also asked you several times to point out any errors in my calculation.

Now you are saying you knew all along that I should have been using a displacement of more than four times that amount and a ratio of 25:1?

I really hope you didn't know that all along, because if you did, and you didn't bring it up, you were simply being a troll. I will give you the benefit of the doubt and assume that you had no idea what the displacement was until you recently figured it out.

More insults, whilst it would be amusing to reply in kind I refuse to lower myself to that level. Most people reading the thread back will conclude that your comments are unjust and uncalled for. Furthermore, your refusal to acknowledge that the power and energy ratings that were stated were infact correct is just a measure of the Geezer. It would also be jolly decent of you to retract the false accusations regarding violations of the laws of thermodynamics.


A possible explanation for my not realising I needed to spell every step out to you sooner could be that you were reluctant to give your calculation or that I'm not rude or perhaps we're speaking a different language - this video might offer a possible explanation  [;)].

http://www.youtube.com/watch?v=6D9Kt0sTWy8 (http://www.youtube.com/watch?v=6D9Kt0sTWy8)

Tallyho old bean!
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/10/2011 12:02:04
Mootle,
What's the reason for not building a scale model?

I have worked up the sketch designs, component selections and costs for a small system (3kW,) which came out at ca. £50k in materials and special pool rental plus my time to build and transport. Having already invested in software and time I think my wife would think me quite selfish to spend this kind of money on my idea rather than the kids college fund. Since the fundamentals of the system are well established I was hoping to get investment for the pilot.

But maybe I should research a design for a micro-scaled model to say power an LED lamp (3W) just to demonstrate the principles. The problem is I would probably have to develop my own turbine and generator set as I couldn't find anything that small on the market.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 24/10/2011 13:47:10
Peter - could you explain the equation you use to get the figure of 2MW - I don't recognize it - but then I probably wouldn't.  It is dimensionally correct - but I cannot quite see the logic behind it.  I would have thought power needed for a pump (or vice vers) would be along the lines of (ignoring efficiency)

power = Δheight * density * flow * gravity -> m * kg.m^-3 * m^3.s^-1 * m.s^-2 -> kg.m^2s^-3

your equation dissects flow into two components cross sectional area and sqrt(2.Δh.g)
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 24/10/2011 14:07:33
If you reverse the equation

power = Δheight * density * flow * gravity and put 2MW in as power generated you find you need to move 345000 cubic metres of water by 50 metres every twenty four hours

2,000,000 = 50m * 1000 * 10 * flow
flow = 4m^3 per second

4m^3 * 60 * 60 * 24 = 345600 m^3 per day
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/10/2011 16:57:23
Imatfaal - I agree, the calculation is less well known as those used by Bored chemist and Geezer but the principles are very similar. I didn't derive the equation, it is something that is commonly used in the field of hydropower. Ignoring efficiency, I would break down the equation as follows: the first element (density * gravity * head) accounts for the static head or pressure.

The balance of the equation Agen*(2*9.81*dLL)^0.5 deals with the dynamic flow, where (2*9.81*dLL)^0.5 is the jet velocity and the product of the pipe area and the velocity is the volumentric flow rate.

Using the figures I gave earlier, you should get a flow rate of:
4.65 m3/s

The product of the two is the theoretical power hence the need for an efficiency. Fortunately, large Pelton Wheel type turbines are efficient energy converters. As a designer you have a choice (limited by the size of the Storage Vessel,) you can have a high power output for a short duration (this might be useful to meet power surges that are predictable,) or a low power output over a longer duration (to meet base load,) or something in between. I opted for the later since this enables the optimum revenue from the Feed in Tariff, a cost effective turbine / generator selection, and it gives time for the ascent and purge phases to occur. For this idea, it is desirable to synchronise the Buoyancy Engine cycle with the tidal pattern. There are a number of key time frames that must be achieved: the Storage Vessel must be purged and ready for the descent phase at the each low tide to allow the maximum energy to be extracted from the tidal rise, the Generation phase must be completed during the tidal fall and give time for the Storage Vessel ascent and purge phases.

For a volume of 67,000m3 this gives ca. 14,400s of flow or 4hr worth of 2MW power generation available twice per day.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 24/10/2011 18:23:29
Peter - OK I worked it out - its just a replacement of the flow by the cross-sectional area multiplied by a rearrangement of the old suvat equation v^2=u^2+2as.

Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 24/10/2011 18:28:24
Just recap on the economics -
1. your tank that sinks must be able to withstand 5 atmospheres pressure and hold 67000m3 of water - being very generous this tank itself will have to be constructed of about 10k mt of steel and will total about 80k m3
2. to drag this to the bottom with a ratio of 25 to 1 your pontoon which is moving by 2m will have to displace around 2M m3
3. you will need miles of steel wire - the breaking strength of a 300m 42mm steel wire rope is about 900k N but the safe working load is around 200k N

1.  your tank will cost 5 million bucks in steel alone
2.  easiest way to get 2M m3 of floating pontoon is to buy 7 vlccs (large tankers not supertankers) - scrap price of about 20 million bucks each
3.  i seem to remember that each SWR costs us about 5,000 bucks and weighs over a tonne- you will be needing lots.  and these are designed for use above sea not underwater. 

Set up costs are well over 150 million bucks lets say £100M - there is just a lot of steel involved

Wholesale electricity prices last month in the uk were £47 per MWh

Your set up generates 16 MWh per day (on your calcs 2MW for 4 hours twice daily) thats an income of £750 per day

To break even at today's prices and not including interest, labour, maintenance, insurance, and downtime you would need to generate 365 days a year for 365 years
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 24/10/2011 19:26:05
This is going nowhere.
Mootle,
Please tell us the numbers you are working from, in particular,
The volume of the floating pontoon,
Its rise and fall distance.
The volume of the moving tank
The number of pulleys or the vertical range of the moving tank.
The number of tides each day.

That is (more than) enough information to work out how much energy is stored each day.
For the sake of this  bit of work we can assume that water is incompressible and has a density of 1 tonne per m^3. We can also assume, to make the maths easy, that the efficiency of the turbine and generator are 100%.

Then we can have a sensible look at
(1) are you actually ignoring the rules of physics and
(2) are you ignoring the rules of economics.

Incidentally, I think for the record, that your equation is correct, provided that you are calculating the right quantity. My best guess is that somewhere or other we are at crossed purposes.
If you can give us the information above then we can all get a better look at the problem.
Imatfaal,
Your dissection of his equation is right when you say.
"your equation dissects flow into two components cross sectional area and sqrt(2.Δh.g)"

the root 2gh factor is the speed at which water would fall if it dropped down a pipe with no viscous losses.
Multiply that by an area and you have cubic metres per second.
Multiply by density and you get mass per second. Multiply by acceleration and you get force per second (an odd unit, but it's legitimate)
Multiply by distance and you get force times distance divided by time; which is work done/ time which is power.

The formula is OK. I think the values put in as the volume etc need clarification.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/10/2011 19:28:30
Just recap on the economics -
1. your tank that sinks must be able to withstand 5 atmospheres pressure and hold 67000m3 of water - being very generous this tank itself will have to be constructed of about 10k mt of steel and will total about 80k m3

2. to drag this to the bottom with a ratio of 25 to 1 your pontoon which is moving by 2m will have to displace around 2M m3
3. you will need miles of steel wire - the breaking strength of a 300m 42mm steel wire rope is about 900k N but the safe working load is around 200k N

1.  your tank will cost 5 million bucks in steel alone
2.  easiest way to get 2M m3 of floating pontoon is to buy 7 vlccs (large tankers not supertankers) - scrap price of about 20 million bucks each
3.  i seem to remember that each SWR costs us about 5,000 bucks and weighs over a tonne- you will be needing lots.  and these are designed for use above sea not underwater. 

Set up costs are well over 150 million bucks lets say £100M - there is just a lot of steel involved

Wholesale electricity prices last month in the uk were £47 per MWh

Your set up generates 16 MWh per day (on your calcs 2MW for 4 hours twice daily) thats an income of £750 per day

To break even at today's prices and not including interest, labour, maintenance, insurance, and downtime you would need to generate 365 days a year for 365 years

Imatfaal - thanks for this, I really need to get some accurate costings.

First of all I would agree that the idea has little scope for value for money if wholesale prices alone are used. Fortunately, government incentives are available for technologies such as this so we can substitute your revenue figure with the ones I gave, i.e., ca. £1m/yr or £2,8k/d including the FIT / RO and Export Values to which I can give references if required. Even so, based on your figure, the platform would need to serve additional functions such as forming a platform for wind turbines, in order to provide a return on investment within a reasonable period of time.

Secondly, whilst I like the idea of using the nearest comparison, I have no reference for the scrap value of a tanker or the Storage Vessel, so will need to research this for myself to gauge the accuracy of the information, but any references your have will be gratefully received. However, there is a lot of scope to value engineer the Pontoon, which in comparison to a tanker would be a far simpler design.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/10/2011 19:38:52
This is going nowhere.
Mootle,
Please tell us the numbers you are working from, in particular,
The volume of the floating pontoon,
Its rise and fall distance.
The volume of the moving tank
The number of pulleys or the vertical range of the moving tank.
The number of tides each day.

I have already given all of this information but once more:
The volume of the floating pontoon = 1,675,000m3
Its rise and fall distance = 2m
The volume of the moving tank = 67,000m3
The number of pulleys or the vertical range of the moving tank = 50m
The number of tides each day = 2.

That is (more than) enough information to work out how much energy is stored each day.
For the sake of this  bit of work we can assume that water is incompressible and has a density of 1 tonne per m^3. We can also assume, to make the maths easy, that the efficiency of the turbine and generator are 100%.

Sea water density is 1,025kg/m3
Generator efficiency is taken as 85%
Refer to calculation given earlier.

Then we can have a sensible look at
(1) are you actually ignoring the rules of physics and
(2) are you ignoring the rules of economics.

Incidentally, I think for the record, that your equation is correct, provided that you are calculating the right quantity. My best guess is that somewhere or other we are at crossed purposes.
If you can give us the information above then we can all get a better look at the problem.


That would be very useful - thank you.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 24/10/2011 20:37:18
This is going nowhere.
Mootle,
Please tell us the numbers you are working from, in particular,
The volume of the floating pontoon,
Its rise and fall distance.
The volume of the moving tank
The number of pulleys or the vertical range of the moving tank.
The number of tides each day.

That is (more than) enough information to work out how much energy is stored each day.
For the sake of this  bit of work we can assume that water is incompressible and has a density of 1 tonne per m^3. We can also assume, to make the maths easy, that the efficiency of the turbine and generator are 100%.

Then we can have a sensible look at
(1) are you actually ignoring the rules of physics and
(2) are you ignoring the rules of economics.

Incidentally, I think for the record, that your equation is correct, provided that you are calculating the right quantity. My best guess is that somewhere or other we are at crossed purposes.
If you can give us the information above then we can all get a better look at the problem.
Imatfaal,
Your dissection of his equation is right when you say.
"your equation dissects flow into two components cross sectional area and sqrt(2.Δh.g)"

the root 2gh factor is the speed at which water would fall if it dropped down a pipe with no viscous losses.
Multiply that by an area and you have cubic metres per second.
Multiply by density and you get mass per second. Multiply by acceleration and you get force per second (an odd unit, but it's legitimate)
Multiply by distance and you get force times distance divided by time; which is work done/ time which is power.

The formula is OK. I think the values put in as the volume etc need clarification.


It should always come back to work done by the tide against the pontoon. The displacement of the pontoon and the elevation of the tide defines the maximum energy that can be produced.

All the other stuff about pressures and flows is in regard to the extraction of the energy, and there are a bunch of ways of doing that, some of which may be more efficient than others. Whether we use Mootle's "Turbine in a giant submarine" approach, pump water up a hill and let it drive a turbine on the way back down, or use BC's pontoon pulling a string idea, might have some effect on the efficiency, but it won't alter the available energy one bit.

A tidal dam works the same way, except the head is the tidal variation. It has the advantage that it can have an enormous "displacement" with a very simple mechanism. Ignoring ecological implications, the downside is that the head is small which means the turbines are rather chunky.

Not having a good handle on the energy input is a bit like trying to design a coal fired power station without having any idea about how much coal it's going to burn. With any tidal system, the displacement (or water elevated) dominates the design and cost. After that, it's "simply" a question of extracting the energy as efficiently as possible.

A water turbine that's designed for the available flow and head should operate with an efficiency of at least 90%, so, to get a reasonable estimate of the energy output we can avoid a huge amount of futzing around by simply multiplying the work done by the tide on the displacement by 0.9

Any calculation that produces a significantly different result is suspect, not to mention mucked up  [:D]
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 24/10/2011 20:47:32
I should have added that Mootle really only needs to specify the pontoon's displacement and the tide height.

EDIT: I forgot to factor in the efficiency of the generator! That might knock off another 10% perhaps? 80% efficiency to get to kWh might be more realistic.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 24/10/2011 22:08:06
Right, now we have an agreed set of data.
The weight of the pontoon is g * rho * V
9.81 m/s/s * 1025 kg/m^3 *  1,675,000m3
So the weight is 1.68 E 10 Newton
It travels up 2 metres on each tide so that's
3.36 E 10 Joules

Lets all agree on something here.
That, if I have got the arithmetic correct, is all the energy that the tide provides to the system, so that's all the energy that could ever hope to get into the turbines and thus to the generator and eventually as electricity. In fact it will be less than that but, since it's not my field, I can't come up with a realistic guess for the efficiency so I will pretend it's 100%. We can always allow for that later.
It does that every 12 hours
i.e. every 43200 seconds

So the mean power is 0.78 MW.

The air conditioning system where I work takes more power than that.
Now you can get that power from this system, but it needs, at the very least a big metal box as the float.
That box has to displace nigh 1.7 million tonnes of water. So it's at least comparable with building some large tankers or buying them as scrap (probably not a great move- they will have been scrapped for a reason). You will need about six of them.
That's roughly $120M

It's never going to pay.

0.78MW
6833 MW Hr per year.
At £47/ MW Hr
£300,000
Lets assume that a bizzare government subsidy pays 5 times the going rate (that's rather more than all your figures added together)
If you  invest $120M or £75M  you could- with no other building costs and no allowance for the other infrastructure like the pulleys , not maintaining it nor building labour.... and with absurdly generous subsidy and assuming 100% efficiency get a return of £1.5M

2%

LOL
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/10/2011 01:15:54
Yes, as I said about a week ago,

Quote
A half million tonne pontoon can only generate 250kW (average)

So a 1.7Mt pontoon will only generate 0.85 MW (average) on that basis. I think I was a bit generous with my rounding. 
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/10/2011 06:33:26
Mootle,
What's the reason for not building a scale model?

I have worked up the sketch designs, component selections and costs for a small system (3kW,) which came out at ca. £50k in materials and special pool rental plus my time to build and transport. Having already invested in software and time I think my wife would think me quite selfish to spend this kind of money on my idea rather than the kids college fund. Since the fundamentals of the system are well established I was hoping to get investment for the pilot.

But maybe I should research a design for a micro-scaled model to say power an LED lamp (3W) just to demonstrate the principles. The problem is I would probably have to develop my own turbine and generator set as I couldn't find anything that small on the market.

I actually agree with Mootle! (Watch for the carefully concealed insults.) There isn't much point in producing a scale model of the turbine end because it's already well known what a water turbine will do at various heads and flow rates, so why bother? Also, turbines don't scale well either, so the results could be very misleading. The pulley system should work too. Why wouldn't it?

The questions are to do with the sheer size of all the working parts, their ability to survive and function in a hostile marine environment, and their cost relative to the power generated. Some of those can only be answered by building a model that is large enough to operate in the hostile marine environment.

I don't think there is any question that the "turbine in a submarine" (subturbine? turbmarine? soupterrine?) could not be made to work, so there isn't much point in modelling that part of the system. What could be done is to model the system with a dummy turbmarine that doesn't produce any power. That would help to keep the cost down, a lot.



 
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/10/2011 07:14:03
Wait a minute! I realized something just after my last post.

Mootle could be short-changing himself. His system is supposed to be tidal, but is it really? There is no doubt that the tide is a major element here, but what about waves?

If the pontoons(s) are not too enormous, they will also be lifted by any ocean swell, and each time the swell lifts the pontoon, the turbmarine (sorry [;D]) will get cranked a bit lower. It might actually descend much faster than we think. It's a question of sizing the pontoon relative to the wavelength of the swell.

I bet Mootle already knew that and he was just waiting to see if we could figure it out. (Oops! I hope I didn't put my foot in it again.)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 15:38:58
I should have added that Mootle really only needs to specify the pontoon's displacement and the tide height.

EDIT: I forgot to factor in the efficiency of the generator! That might knock off another 10% perhaps? 80% efficiency to get to kWh might be more realistic.

Most mathematicians (worth their salt at least,) would run check calculations - this is a healthy thing for engineers to do as well, so I'm grateful for the grilling. As it is we have now completed three checks and it has been demonstrated that the original claims are sound. Once again, I apologise for my part in the misunderstanding by not making it clearer in my presentation. It would be good to move forward, if we can so that our time here is used productively.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 25/10/2011 16:09:38
I should have added that Mootle really only needs to specify the pontoon's displacement and the tide height.

EDIT: I forgot to factor in the efficiency of the generator! That might knock off another 10% perhaps? 80% efficiency to get to kWh might be more realistic.

Most mathematicians (worth their salt at least,) would run check calculations - this is a healthy thing for engineers to do as well, so I'm grateful for the grilling. As it is we have now completed three checks and it has been demonstrated that the original claims are sound. Once again, I apologise for my part in the misunderstanding by not making it clearer in my presentation. It would be good to move forward, if we can so that our time here is used productively.

Peter - I speak as a company executive who proposes, evaluates, and decides upon projects of this sort of size - your proposal is not sound. 

Even using the most generous evaluations of set-up costs, zero running costs, and "free" tidal energy this idea will not make money and would be a burden upon any authority that tried to promote it.

1.  Tidal power obtained through a floating pontoon could be better harnessed through land based power generation (per BC suggestion or others)
2.  Most places with significant tides also have significant currents - this will add to the cost - but more importantly to the danger.  You will have SWR under working loads - add currents to this and you have the risk of breaking cables.  You will need mariners and engineers on site to deal with problems and these men's safety has to be paramount - most masters would not dream of tying up alongside another vessel in open seas, let alone a complicated system of tying both to the ocean floor and to other sections of the floating pontoon
3.  the environmental impact would be vast - you are talking about a fifth of a million tonnes of steel in the ocean.  all of which need anti-fouling, anti-corrosion, and regular structural integrity checks.

All in all it is a huge undertaking, expensive and technically difficult. 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 16:13:51
Right, now we have an agreed set of data.
The weight of the pontoon is g * rho * V
9.81 m/s/s * 1025 kg/m^3 *  1,675,000m3
So the weight is 1.68 E 10 Newton
It travels up 2 metres on each tide so that's
3.36 E 10 Joules

Lets all agree on something here.
That, if I have got the arithmetic correct, is all the energy that the tide provides to the system, so that's all the energy that could ever hope to get into the turbines and thus to the generator and eventually as electricity. In fact it will be less than that but, since it's not my field, I can't come up with a realistic guess for the efficiency so I will pretend it's 100%. We can always allow for that later.
It does that every 12 hours
i.e. every 43200 seconds

So the mean power is 0.78 MW.

The air conditioning system where I work takes more power than that.
Now you can get that power from this system, but it needs, at the very least a big metal box as the float.
That box has to displace nigh 1.7 million tonnes of water. So it's at least comparable with building some large tankers or buying them as scrap (probably not a great move- they will have been scrapped for a reason). You will need about six of them.
That's roughly $120M

It's never going to pay.

0.78MW
6833 MW Hr per year.
At £47/ MW Hr
£300,000
Lets assume that a bizzare government subsidy pays 5 times the going rate (that's rather more than all your figures added together)
If you  invest $120M or £75M  you could- with no other building costs and no allowance for the other infrastructure like the pulleys , not maintaining it nor building labour.... and with absurdly generous subsidy and assuming 100% efficiency get a return of £1.5M

2%

LOL


I'm glad that we now have a comparable view of the systems energy and rating.

Based on your financial analysis no renewable energy system would get off the ground. In fact I doubt any traditional system would either. The challenge is to get a Return on Investment, RoI within a reasonable time period. I've indicated the revenue for (10) systems (enough power for your AC and then some,) for a 20yr period as this is the period that the incentives are available for. Retail energy costs are assumed to be fixed but based on the past 12 months this is likely to be a very conservative estimate. For the idea to have a reasonable RoI the total cost would need to be less than say £100m for the (10) systems or the revenue of £208m would need to be increased to account for any cost beyond that. I haven't began to cost the system yet but experience tells me that even with best value engineering the revenue will need to be increased. Whilst wind and solar are not as reliable as this tidal system they may offer improved RoI's if the pontoon is engineered to serve multiple functions. I've noticed a number of floating offshore wind proposals around so this isn't as far fetched as it might seem. The benefit is that such a mix would improve reliability.

You might think the incentives are 'bizarre' but the reality is that we need to replace our current systems and developing new ideas costs money!

The system processes have good synergy with low cost hydrogen or fresh water production. In the future it likely that both resources will become valuable commodities.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 16:30:28

Wait a minute! I realized something just after my last post.

Mootle could be short-changing himself. His system is supposed to be tidal, but is it really? There is no doubt that the tide is a major element here, but what about waves?

If the pontoons(s) are not too enormous, they will also be lifted by any ocean swell, and each time the swell lifts the pontoon, the turbmarine (sorry [;D]) will get cranked a bit lower. It might actually descend much faster than we think. It's a question of sizing the pontoon relative to the wavelength of the swell.

I bet Mootle already knew that and he was just waiting to see if we could figure it out. (Oops! I hope I didn't put my foot in it again.)
[/quote]

Mootle could be short-changing himself. His system is supposed to be tidal, but is it really? There is no doubt that the tide is a major element here, but what about waves?

If the pontoons(s) are not too enormous, they will also be lifted by any ocean swell, and each time the swell lifts the pontoon, the turbmarine (sorry [;D]) will get cranked a bit lower. It might actually descend much faster than we think. It's a question of sizing the pontoon relative to the wavelength of the swell.

I bet Mootle already knew that and he was just waiting to see if we could figure it out. (Oops! I hope I didn't put my foot in it again.)


I'm sorry to dash your spirits but the idea started with wave theorem. This is an active topic of research in itself, I was especially interested in one company which is developing wave prediction technology, that could be used in conjunction with renewable wave power technology amongst other applications.

However, I soon realised that for a meaningful power output, wave power could not play a big part for the Buoyancy Engine, mainly because the Pontoon will be so big. This is made worse since it is beneficial for the Pontoon to be a shallow profile, i.e., cover a wide area in order to minimise sinkage losses.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 17:31:18
I should have added that Mootle really only needs to specify the pontoon's displacement and the tide height.

EDIT: I forgot to factor in the efficiency of the generator! That might knock off another 10% perhaps? 80% efficiency to get to kWh might be more realistic.

Most mathematicians (worth their salt at least,) would run check calculations - this is a healthy thing for engineers to do as well, so I'm grateful for the grilling. As it is we have now completed three checks and it has been demonstrated that the original claims are sound. Once again, I apologise for my part in the misunderstanding by not making it clearer in my presentation. It would be good to move forward, if we can so that our time here is used productively.

Peter - I speak as a company executive who proposes, evaluates, and decides upon projects of this sort of size - your proposal is not sound. 

Even using the most generous evaluations of set-up costs, zero running costs, and "free" tidal energy this idea will not make money and would be a burden upon any authority that tried to promote it.

1.  Tidal power obtained through a floating pontoon could be better harnessed through land based power generation (per BC suggestion or others)

You may prove to be right based on the current presentation. However, whilst I value your input before I give the idea up I need to work this thing through to a conclusion one way or the other. This includes value engineering and costing a scaled model and looking at ways to improve the revenue.

2.  Most places with significant tides also have significant currents - this will add to the cost - but more importantly to the danger.  You will have SWR under working loads - add currents to this and you have the risk of breaking cables.  You will need mariners and engineers on site to deal with problems and these men's safety has to be paramount - most masters would not dream of tying up alongside another vessel in open seas, let alone a complicated system of tying both to the ocean floor and to other sections of the floating pontoon

There are a number of associated acronyms for SWR, please advise which one you mean to allow me to directly address that concern.

As for safety of the operators I would entirely agree that their safety is paramount. I would not allow any design carrying my name to reach the market without an indepth design, construction and operation risk assessment. This would include compliance with associated regulations and collaboration with marine experts and Ship Masters alike. I would expect this to include: tension monitoring of the cables and anchorages, position monitoring of Cables / Storage Vessel / Pontoon in order to alarm in the event of any operation outside of design tolerance. Cables would be designed for the dynamic loading including plenty of redundancy. I would tend to follow existing protocols for oil rig maintenance, i.e., all systems would be within helicopter range although ship to Pontoon transfer would be facilitated via rib. I would foresee living accommodation pods for longer stay. All power technologies carry risk (Exxon Valdez oil spill,Fukushima Daiichi nuclear disaster...) and this is no exception. Fail-safe mode would need to be carefully considered and incorporated into the costings. For instance, the reason I'm looking toward submarine design is that the separate ballast / main storage tank, SV i.e., if there was an issue with the SV ascending too quickly the ballast tanks could be used as a secondary means to regulate the rate of ascent - if that doesn't work there would also be a skuttle option (recovery options would be engineered). The Pontoon would be tethered to cater for a loss of tension....

I haven't got around to evaluating the risks in depth but to date haven't seen anything that was beyond mitigation.

3.  the environmental impact would be vast - you are talking about a fifth of a million tonnes of steel in the ocean.  all of which need anti-fouling, anti-corrosion, and regular structural integrity checks.

All in all it is a huge undertaking, expensive and technically difficult. 

I agree, this is not a small undertaking but as an engineer I love a good challenge. Whilst steel will obviously form a part of the structure, the value engineering will establish the best use of materials. I've already covered a number of the issues but please quote against any reply which didn't go into sufficient detail. In environment terms I would be keen to evaluate the carbon return rate, i.e., care would be taken to manage the embedded carbon of the system as well as the financial cost. Part of the Environmental Impact Assessment would be to use materials that are conducive to establishing and encouraging marinelife. I've followed various studies including skuttling of ships and coral reef promotion which have enhanced the environment rather than detract. I would look to collaborate with the teams who were involve such that the Pontoon design would effectively become a sanctuary for wildlife.

Thank you for your input, it really helps me to understand the issues that prospective investors will be interested in.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 25/10/2011 18:25:50
SWR = Steel Wire Rope

Peter - I think we all appreciate your enthusiasm for this, but you are missing all the power-economic realities involved. 

As one mad example - I have suggested using old ships as your pontoon (I really think you would struggle to find anything even close in price that could withstand years at sea).  Even if you could pick up 7 large tankers FOR FREE - if we assume that you have to move the ships an average of 2000nm to install them (which is fairly generous, eg sale could be in England but more likely in India) then you have to put into consideration the fuel cost.  You would have to burn about 4000 barrels of fuel oil to get the ships that distance - that's about 6750 MWh worth of fuel.  In either an economic or a carbon review it soon shows that even getting the ships in position costs more in energy than your system produces in a year! 

we need either cheap systems that generate small "household size" amounts of power - or expensive systems that generate large "town size" amounts of power; but expensive set-ups that provide only tiny power returns are just a waste of time, money, and probably energy.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 19:02:51
SWR = Steel Wire Rope

Peter - I think we all appreciate your enthusiasm for this, but you are missing all the power-economic realities involved. 

As one mad example - I have suggested using old ships as your pontoon (I really think you would struggle to find anything even close in price that could withstand years at sea).  Even if you could pick up 7 large tankers FOR FREE - if we assume that you have to move the ships an average of 2000nm to install them (which is fairly generous, eg sale could be in England but more likely in India) then you have to put into consideration the fuel cost.  You would have to burn about 4000 barrels of fuel oil to get the ships that distance - that's about 6750 MWh worth of fuel.  In either an economic or a carbon review it soon shows that even getting the ships in position costs more in energy than your system produces in a year! 

we need either cheap systems that generate small "household size" amounts of power - or expensive systems that generate large "town size" amounts of power; but expensive set-ups that provide only tiny power returns are just a waste of time, money, and probably energy.

Your idea to use old stock was useful in that it gives a useful budget but I don't think this would be useful for a working solution. The design would have to be bespoke to cater for the forces involved and the function, although lessons learned would be taken from a number of vessels that approximate to the desired function. All things considered a new build approach would be best.

I have researched various types of cable systems, there are a number of options including synthetic and cast iron. I will investigate the options further as part of the scaled application but as I indicated earlier the safe loading and testing of cables can all be managed through planned maintenance regimes.

All renewables technologies seem to have one thing in common, they only start to make sense when they are scaled up and even then nothing can be taken for granted and the particular circumstances have to be fully considered. Economies of scale is really important and the kind of reality check you guys are giving is much appreciated. However, having been involved in many renewable schemes, I tend to remain open minded until all avenues have been explored. 

I agree with much of the advice that has been given and that this would not be a venture without its challenges.

Then again nobody ever said it would be easy!
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 25/10/2011 19:28:09
The forum software does not support a large enough font size to be appropriate for the word "Bollocks!"  in response to " As it is we have now completed three checks and it has been demonstrated that the original claims are sound. ".
 Ditto "Based on your financial analysis no renewable energy system would get off the ground.".

" I haven't began to cost the system yet "
You don't need to. We already did and it's goosed before it starts.
"For the idea to have a reasonable RoI the total cost would need to be less than say £100m for the (10) systems"
But the cost is more than that for 1 system, never mind 10.
And the only way for the revenue to rise is for the price of electricity to rise. Now, just before you say "OK, All I have to do is wait", remember that much of the cost of the project is an indirect energy cost. For example it takes lots of energy to make steel or concrete so, if the price of energy rises, so does the cost of the project.
This will never work.

When you say "You might think the incentives are 'bizarre' but the reality is that we need to replace our current systems and developing new ideas costs money! " you are missing the point.
It's true that, for example, early solar cells were so expensive that only NASA used them (and it didn't use more than it could get away with). Decades of research means that solar cells are nearly competitive  with more conventional power. Perhaps they are better value than coal fired electricity if you consider the cost of transmission and  global warming (and I'm just not getting into that debate here: if you are unhappy about it, just remember I started the sentence with "perhaps").

They needed new ideas and, as you say, "developing new ideas costs money".
But your idea isn't new.
There's nothing about it that is not mature technology.
Ropes, pulleys, and barges have been around for a while. Even hydroelectric generators are not new.

What developments would you put on your "wish list" that would actually make your system anything other than a white elephant?

Furthermore, you seem not to have noticed that not all things benefit from economies of scale.
Making your design 10 times bigger makes it more than 10 times more expensive, but only produces 10 times more power. The reason it gets more expensive is the law of diminishing returns. If I want to buy a used tanker I will get the cheapest one I can find that still floats, it will cost me X million, but if I want to buy another tanker  t will cost more (because I already bought the cheapest one). The sixth tanker is going to cost me a lot more than the first. Your "plan" calls for something like 60.
I doubt there are 60 scrap oil tankers on the market at any time, so you will have to start buying newer ones to make your project bigger. The power output increases linearly with the number of ships but the cost increases faster than that.
The bang per buck falls as the system gets bigger.

On a good day with a following wind you might convince me that this system would be viable in the Antarctic, but only on a smallish scale. A research station might be able to get by on 250KW.
You could use an iceberg instead of old oil tanker.
In principle the idea is non polluting, and politically, that might make it an acceptable power source where people really really don't want a diesel spill.

It still wouldn't compete with mains electricity prices in the UK- but it might be cheaper than 12000 miles of extension leads.

There may be some other niche market for this but that's the opposite of an economy of scale.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/10/2011 20:10:20
Perhaps we should lock this thread before it becomes contentious?  [:D]

After all, it's really just a promotional plug for Mootle's patent. Mind you, the feedback he's getting isn't exactly what you'd call "promotional" so we probably don't need to worry about that.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 25/10/2011 20:50:51
Since this discussion is public domain information, his chances of patenting it are less than the chances of it making any money.
It would seem impolite to lock it without giving him a last chance to defend it and I'd hate to start another of those "The establishment are against me! Look! they even locked my thread!" farces. (I know, they usually use more exclamation marks, but I can't bring myself to do that, even for effect)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 22:05:26
..." I haven't began to cost the system yet "
You don't need to. We already did and it's goosed before it starts.
"For the idea to have a reasonable RoI the total cost would need to be less than say £100m for the (10) systems"
But the cost is more than that for 1 system, never mind 10.
And the only way for the revenue to rise is for the price of electricity to rise. Now, just before you say "OK, All I have to do is wait", remember that much of the cost of the project is an indirect energy cost. For example it takes lots of energy to make steel or concrete so, if the price of energy rises, so does the cost of the project.
This will never work.

The system hasn't been costed and even the budget costs that were suggested are open to debate. For instance here http://www.marinelog.com/index.php?option=com_content&view=article&id=1280:increasedscrapping30august2011j01&catid=1:latest-news&Itemid=107 some indicative costs are given for VLCC's. A 2000 281,050DWT measuring 330m*60 is valued at $36m. The height is not given but I would guess somewhere between 50 - 100m, or 990,000m3 - 1,980,000m3, i.e., only one would be needed  - but as per previous posts I would not persue the idea to modify, the system would need to be a new build. There are many possibilities to value engineer and increase revenue but since you seem have disregarded the examples given I will not expand on the point. You will note from the description given in the link that this tanker is double skinned to provide protection from spillage. The Pontoon would not require an expensive propulsion or fuelling system, it only requires a single skin plus gantries, although it would be a sensible precaution to compartmentalise. Also, the DWT is what it can safely carry whereas the ideal Pontoon would be almost entirely immersed when loaded.


When you say "You might think the incentives are 'bizarre' but the reality is that we need to replace our current systems and developing new ideas costs money! " you are missing the point.
It's true that, for example, early solar cells were so expensive that only NASA used them (and it didn't use more than it could get away with). Decades of research means that solar cells are nearly competitive  with more conventional power. Perhaps they are better value than coal fired electricity if you consider the cost of transmission and  global warming (and I'm just not getting into that debate here: if you are unhappy about it, just remember I started the sentence with "perhaps").

They needed new ideas and, as you say, "developing new ideas costs money".
But your idea isn't new...

I agree, bringing global warming into this debate wouldn't be helpful. I'm developing the idea because resources are running out for conventional power generation.

As explained the idea is currently patent pending and the searches indicate that it is a new idea but we will await the outcome of the process to see if the patent is awarded. Solar PV is still a poor investment (in the UK) unless FIT's are taken into account.



There's nothing about it that is not mature technology.
Ropes, pulleys, and barges have been around for a while. Even hydroelectric generators are not new.

What developments would you put on your "wish list" that would actually make your system anything other than a white elephant?

I agree, the technology and know how already are well tested for many of the elements of the idea - this is good news, but there are various aspects of this application that we haven't touched on that would require development.


Furthermore, you seem not to have noticed that not all things benefit from economies of scale.
Making your design 10 times bigger makes it more than 10 times more expensive, but only produces 10 times more power. The reason it gets more expensive is the law of diminishing returns. If I want to buy a used tanker I will get the cheapest one I can find that still floats, it will cost me X million, but if I want to buy another tanker  t will cost more (because I already bought the cheapest one). The sixth tanker is going to cost me a lot more than the first. Your "plan" calls for something like 60.
I doubt there are 60 scrap oil tankers on the market at any time, so you will have to start buying newer ones to make your project bigger. The power output increases linearly with the number of ships but the cost increases faster than that.
The bang per buck falls as the system gets bigger.

This point has already been covered earlier - this is a new build project and most suppliers do tend to reduce their selling price when they have a larger order to deal with.


On a good day with a following wind you might convince me that this system would be viable in the Antarctic, but only on a smallish scale. A research station might be able to get by on 250KW.
You could use an iceberg instead of old oil tanker.
In principle the idea is non polluting, and politically, that might make it an acceptable power source where people really really don't want a diesel spill.

It still wouldn't compete with mains electricity prices in the UK- but it might be cheaper than 12000 miles of extension leads.

There may be some other niche market for this but that's the opposite of an economy of scale.

Interesting but sadly there are few opportunities for tidal in the Antarctic owing to the lack of tidal range (refer to link). My focus is on the UK where there are good opportunities owing to the continental shelf.

http://www.seafriends.org.nz/oceano/tides.htm
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 22:10:17
Since this discussion is public domain information, his chances of patenting it are less than the chances of it making any money.
It would seem impolite to lock it without giving him a last chance to defend it and I'd hate to start another of those "The establishment are against me! Look! they even locked my thread!" farces. (I know, they usually use more exclamation marks, but I can't bring myself to do that, even for effect)

You & Geezer do make me smile  [::)]

I really don't mind a harsh review (once the facts support,) or even profanities after all you only let yourself down.

As I said a while back, I'm happy to step back from this thread for the time being whilst I develop the idea.

Once again, many thanks for your input.

BTW if your gearbox idea does turn out to be beneficial and the idea does confound your expectations and go onto make money I will be sure to recognise your contribution.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/10/2011 22:23:13
Perhaps we should lock this thread before it becomes contentious?  [:D]

After all, it's really just a promotional plug for Mootle's patent. Mind you, the feedback he's getting isn't exactly what you'd call "promotional" so we probably don't need to worry about that.

Interesting, promotion was the last thing I was considering - the presentation isn't ready for that and I would not consider a forum like this as a good place to promote once it is. However, you should realise that promotion works both ways and perhaps one lesson you could learn from this is not to be so quick to assume that people posting know less than you. Instead you could make room for genuine posters who simply want to conduct an honest review of an idea to help with development, because they believe many minds are better than one.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 26/10/2011 00:40:26
Perhaps we should lock this thread before it becomes contentious?  [:D]

After all, it's really just a promotional plug for Mootle's patent. Mind you, the feedback he's getting isn't exactly what you'd call "promotional" so we probably don't need to worry about that.

Interesting, promotion was the last thing I was considering - the presentation isn't ready for that and I would not consider a forum like this as a good place to promote once it is. However, you should realise that promotion works both ways and perhaps one lesson you could learn from this is not to be so quick to assume that people posting know less than you. Instead you could make room for genuine posters who simply want to conduct an honest review of an idea to help with development, because they believe many minds are better than one.

An honest review is only likely to be conducted on an honest and complete design specification. If a design is presented with an incomplete specification, the reviewers are obviously going to conclude that the design is also incomplete.

The lesson is that if you want a proper review, present proper data.

Mootle, I've already asked you to send me your observations by PM. Any more in-thread "editorials" and this thread will be locked.

Now, does anyone wish to add anything that helps to answer the question,

"Will this buoyancy engine-based generator work?"
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 26/10/2011 10:48:33

The system hasn't been costed and even the budget costs that were suggested are open to debate. For instance here http://www.marinelog.com/index.php?option=com_content&view=article&id=1280:increasedscrapping30august2011j01&catid=1:latest-news&Itemid=107 some indicative costs are given for VLCC's. A 2000 281,050DWT measuring 330m*60 is valued at $36m. The height is not given but I would guess somewhere between 50 - 100m, or 990,000m3 - 1,980,000m3, i.e., only one would be needed  - but as per previous posts I would not persue the idea to modify, the system would need to be a new build. There are many possibilities to value engineer and increase revenue but since you seem have disregarded the examples given I will not expand on the point. You will note from the description given in the link that this tanker is double skinned to provide protection from spillage. The Pontoon would not require an expensive propulsion or fuelling system, it only requires a single skin plus gantries, although it would be a sensible precaution to compartmentalise. Also, the DWT is what it can safely carry whereas the ideal Pontoon would be almost entirely immersed when loaded.


What sort of engineer in this field thinks that a vessel that can carry 281 thousand tonnes has a displacement of 1.9 million tonnes!

  I told you that you needed about 7 vlccs and you do.  The deadweight - as I think I already mentioned - is the usable displacement (the total displacement less the steel weight, constants, and a safety margin).  The displacement of the tenzan will be about 360000 mt - but it will have about 25-30000 mt of steel, extras and you need a safety margin.  the double skin nature of takners does not massively increase the amount of steel needed - as the construction methods were changed to use the structural integrity of the double skin rather than needing extensive interior tank walls.   

For a new build you need to put your steel costs up by around 30-50 % and yard space will double the cost.   

Quote
This point has already been covered earlier - this is a new build project and most suppliers do tend to reduce their selling price when they have a larger order to deal with.

Not really no - in the consumer market perhaps - but in the commercial world most prices have been driven pretty far down already.  If one project requires 10000 metric tonnes of steel you might be able to negotiate a few tens of dollars off your price if order 10 - but you ain't gonna get much, both the steel mill and the building yard are already operating on very slim margins

Quote
I agree, bringing global warming into this debate wouldn't be helpful. I'm developing the idea because resources are running out for conventional power generation.

You do not seem to understand the minuscule amount of energy this produces - you would need 20,000 of them to balance just the UK's oil use (let alone our coal and our gas) - thats about one every 500 yards around the entire country!

WE do need "blue sky thinking" - but we need to be hard-nosed over which projects to bin.  There are easier, more efficient, and safer ways to exploit tidal power


Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/10/2011 11:05:08

...Mootle, I've already asked you to send me your observations by PM. Any more in-thread "editorials" and this thread will be locked....

It was a very kind offer but I didn't realise that we were breaking any house rules?

As far as I'm concerned this thread has been a simple series of Q&A's for which I'm most grateful.

Lock the thread or leave it to run its course - I really don't mind, either way I'm sure you will have your reasons.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/10/2011 12:06:33
What sort of engineer in this field thinks that a vessel that can carry 281 thousand tonnes has a displacement of 1.9 million tonnes!

  I told you that you needed about 7 vlccs and you do.  The deadweight - as I think I already mentioned - is the usable displacement (the total displacement less the steel weight, constants, and a safety margin).  The displacement of the tenzan will be about 360000 mt - but it will have about 25-30000 mt of steel, extras and you need a safety margin.  the double skin nature of takners does not massively increase the amount of steel needed - as the construction methods were changed to use the structural integrity of the double skin rather than needing extensive interior tank walls. 

The Pontoon will not bare a significant resemblance to the vessel design upon which a budget comparison is being drawn and as such I would not consider such a vessel for reuse in this application. You are correct that based on DWT (7) vessels would be required (I'm sorry if I gave the wrong impression,) but since the Pontoon would not be constrained by the same sets of legislation / functionality I would anticipate various opportunities in the design / choice of materials etc., that will significantly reduce the gross volume of the Pontoon to achieve the required buoyancy.


For a new build you need to put your steel costs up by around 30-50 % and yard space will double the cost.
Quote

As previously indicated, steel would form part of the design but I would look to employ alternate materials to augment the Pontoon construction.

You do not seem to understand the minuscule amount of energy this produces - you would need 20,000 of them to balance just the UK's oil use (let alone our coal and our gas) - thats about one every 500 yards around the entire country!

WE do need "blue sky thinking" - but we need to be hard-nosed over which projects to bin.  There are easier, more efficient, and safer ways to exploit tidal power

I think this type of tidal energy storage has a place in the future energy mix. Hydropower does already exist but there are limited opportunities available for this in the UK. Once I have some meaningful costings and have reviewed the revenue potential I would look to compare with similarly rated dam projects.

I would agree that this technology alone would not be a suitable to replace oil and it goes without saying that the business case must stack up. I just think it is too early to draw conclusions at this time.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 26/10/2011 19:28:28
"The Pontoon will not bare a significant resemblance to the vessel design upon which a budget comparison is being drawn"
I rather suspect it will. It might be more square in plan and it won't need a pointy front end, but essentially a ship is a big box that floats and so is your pontoon.
The shipwrights have spent the whole of history learning how to do that. If you think you can do better I'm willing to bet you are mistaken.

I asked earlier what you would like future development to improve on so this idea becomes viable.
I'm still waiting.
You can't change the tide and, as I have said, a rise in electricity cost won't help much.
All you can change are the construction materials and the method.
However those materials and methods have been with us for decades (at least) and millennia in some cases.
Do you really foresee an order of magnitude drop in the price of steel?
Do you think that the concrete that holds the pulleys down will become cheaper to make or pour?

Clearly, to make your idea work there has to be a major change somewhere and that change has to make your system a lot cheaper.

What do you think can make it work?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 26/10/2011 20:30:32
For a bit of levity, I was about to make a phony post by Sheepy (who had to temporarily "borrow" Geezer's account) suggesting that "ewe might use a lot of balloons" when it struck me that there could be a problem here.

Hopefully Mootle already has it figured out, but, as I see it, you couldn't actually use a supertanker (or whatever the "official" nautical jargon is according to Admiral Matt). A supertanker (wash my mouth out with soap and water) is only capable of displacing its er, displacement, when it's full of a liquid.

If you were to attach a whopping great cable to a rather large eyebolt on the bottom of an empty supertanker's (wash etc) hull and drag it down towards the seabed, I'm PD sure the ensemble would fold like a cheap suit, bow up, stern up, midships submerged, assuming it didn't immediately split in two.

A loaded supertanker (yeah, yeah yeah) is a lot more like a constrained blob of oil than a solid object. On the other hand, the pontoon has to be submerged with pretty much nothing in it. That suggests to me that it's going to need a lot more steel to prevent it from collapsing, or maybe Sheepy had the right idea.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 26/10/2011 22:04:21
To be fair (and to stop myself looking silly for saying the pontoon is a lot like a ship) ships are actually quite strong. They need to be because, from time to time, they find themselves with the ends held up by waves and with nothing holding up their middles.
It might need to be a bit stronger than a ship but not much. Also, there would be several damn great eye bolts along the hull so the load would be distributed a bit.
It's still not going to work unless there's some magic change in the economics so I'd still like to see Mootle's answer to my question.
What can you change to make this idea work?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 26/10/2011 23:28:25
To be fair (and to stop myself looking silly for saying the pontoon is a lot like a ship) ships are actually quite strong.

True, but they are not submarines. On the other hand, pontoons are sort of shallow depth submarines. They have to displace water with something a lot less dense (probably air) in order to exert a force on the cable. I'm not an expert by any means, but I seem to remember that large tankers rely on their contents to limit the stress on their hulls when they are submerged, and that won't work with a pontoon cos it would sink when the cable pulled on it [:D]

(Obviously, I was being silly with the single eyebolt to make the point.)
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 27/10/2011 10:37:09
to be fair both BC and Geezer are correct.  When a ship is correctly loaded within design parameters they are very tough and will ride out unbelievable seas in the North Atlantic and the Southern Oceans.  But - misloading or loading a cargo outside design parameters will rapidly cause the vessel to crack.

large ships draw a fair amount of water - but not enough I believe to make the structure overly weak when at full draft without cargo (ie forced further into the water without being filled with cargo). A vlcc will be around 15m deeper in the water when fully laden compared to a safe ballast and 18m deeper than being completely empty.  Whilst these ships do rely on the support of water to an extent - they are quite capable of being taken from the water and propped up on blocks for a few weeks every couple of years. 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 27/10/2011 12:12:59
"The Pontoon will not bare a significant resemblance to the vessel design upon which a budget comparison is being drawn"
I rather suspect it will. It might be more square in plan and it won't need a pointy front end, but essentially a ship is a big box that floats and so is your pontoon.

The shipwrights have spent the whole of history learning how to do that. If you think you can do better I'm willing to bet you are mistaken.


I've tried to describe it to you but evidently without much success - it will all become clear once I've completed the scaled model if the house rules permit me to post it but as it stands it would be unfair for me to take your bet.

I asked earlier what you would like future development to improve on so this idea becomes viable.
I'm still waiting.
You can't change the tide and, as I have said, a rise in electricity cost won't help much.
All you can change are the construction materials and the method.
However those materials and methods have been with us for decades (at least) and millennia in some cases.
Do you really foresee an order of magnitude drop in the price of steel?
Do you think that the concrete that holds the pulleys down will become cheaper to make or pour?

Clearly, to make your idea work there has to be a major change somewhere and that change has to make your system a lot cheaper.

What do you think can make it work?


As I've said before there are many developmental steps required.

I agree, steel prices are only likely to go up with time (as energy costs soar). This is one reason for aiming to minimise the use of steel in the system design.

One of the biggest challenges will be the anchorage. I don't think the use of large quantities of concrete will be sustainable or cost effective. I'm working on a construction animation to show the sequences involved and would post this in due course - house rules permitting.

The system design will benefit from a flat pontoon structure. Since the hydraulic forces will be modest (compared with the Storage Vessel,) I'm researching the possibility of reinforced plastics for the main base. The challenge is to effectively spread the forces - time and a bit of FEA will tell.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/10/2011 17:16:04
but not enough I believe to make the structure overly weak when at full draft without cargo (ie forced further into the water without being filled with cargo).

But how would you know? Have you ever seen a ship at full draft without any cargo (or ballast) [;D]

That's really my point. Ships are not designed to be submarines.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/10/2011 17:44:58
One of the biggest challenges will be the anchorage.

Friction could be just as bad. A 25:1 "block and tackle" has so much friction that it may offer no mechanical advantage over one with a much lower ratio. When you turn a 25:1 around and try to use it as a 1:25, there could be so much friction that the storage vessel won't budge and something will break instead.

Using gears instead of pulleys doesn't help much either.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 27/10/2011 18:56:37
"I'm researching the possibility of reinforced plastics for the main base."
Do you think you will have some miraculous insight that has eluded the designers of things like bridge footings for millennia?

Seriously, if they still use concrete for building things like the Thames Barrier, why do you think plastic might be better?
Do you think they are idiots?
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 27/10/2011 19:08:36
"I'm researching the possibility of reinforced plastics for the main base."
Do you think you will have some miraculous insight that has eluded the designers of things like bridge footings for millennia?

For the main base of the Pontoon.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/10/2011 19:45:45
"I'm researching the possibility of reinforced plastics for the main base."
Do you think you will have some miraculous insight that has eluded the designers of things like bridge footings for millennia?

For the main base of the Pontoon.

Yes, that's a big problem. Despite the statements of my learned colleagues Imatture and Bruised Chemist (who obviously couldn't engineer their way out of a paper bag) distributing the enormous force in the cable evenly over something with an enormous surface area like a pontoon (or a big honking boat) is a non trivial problem. And don't be fooled into thinking that distributing the pulleys will solve that problem either. The aforementioned friction will ensure that it won't.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 27/10/2011 22:01:18
http://xkcd.com/969/
seems like an odd coincidence.
Anyway,
Whatever Mootle.
You can dream on. The laws of physics and economics are still going to be there when you wake up.
the pulleys are not just a source of friction, but pointless. If you have not worked out why then I don't think you are going to get much further with this.


Incidentally, Geezer, our views may differ, but the outcome is the same.
I think that he will need the pontoon to be built quite a lot like a boat because it's quite like a boat i.e. it is subject to huge stresses and it has to float.
You think it will be different from a boat because the forces will  be in essentially the opposite direction and point loads rather than distributed loads; which is fair enough.

When it comes down to it, what he will need will be a big strong floaty thing. He certainly won't get that any cheaper than a boat, so his price structure is dead in the water.
Perhaps he should fit it with some ropes and pulleys.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/10/2011 22:44:08
When it comes down to it, what he will need will be a big strong floaty thing.

Actually, it really does not need to be all that strong. It could just be a biggish block of expanded polystyrene (like the one under the floor of my boat). The tricky bit is connecting it to the cable  [:)]
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/10/2011 23:12:56
Of course, you could eliminate the need for a big strong floaty thing entirely if you used the variation in head to pump water up a hill insted. That would also eliminate the need for a mechanical gearing system because hydraulic systems let you swap head for volume and vice-versa.

Unfortunately, you might end up with something that looked a lot like this

 [ Invalid Attachment ]


Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 28/10/2011 06:58:27
A big strong non-floaty thing.
But the fish are smiling so it must be OK.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 28/10/2011 11:09:13
"I'm researching the possibility of reinforced plastics for the main base."
Do you think you will have some miraculous insight that has eluded the designers of things like bridge footings for millennia?

For the main base of the Pontoon.

Yes, that's a big problem. Despite the statements of my learned colleagues Imatture and Bruised Chemist (who obviously couldn't engineer their way out of a paper bag) distributing the enormous force in the cable evenly over something with an enormous surface area like a pontoon (or a big honking boat) is a non trivial problem. And don't be fooled into thinking that distributing the pulleys will solve that problem either. The aforementioned friction will ensure that it won't.

You are correct, to achieve an efficient 25:1 pulley for this application will be quite an engineering challenge. In this way, the pulley system would be another of those developmental areas.

Friction is a function of:

The quality of the pulley bearings.
Diameter of the pulley.
Slippage between the cable and the pulley.
Material selection for the cable.
Bend radius of the cable....

The strength of the cable would be a constraining factor, once the SWL is established for a suitable marine cable the number of pulleys would be determined from the total load (including dynamic loads,) and a sensible margin of safety (including redundancy).
 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 28/10/2011 11:41:46
....You can dream on. The laws of physics and economics are still going to be there when you wake up.
the pulleys are not just a source of friction, but pointless. If you have not worked out why then I don't think you are going to get much further with this...

I thought we had got to the bottom of the 'laws of physics' - are you still questioning my claims?

We don't have the necessary information to answer the question of economics but basing this on the value of existing vessels is flawed. These vessels are designed with a particular function in mind. The pontoon has a very different set of constraints and this opens up a wide array of possibilities to value engineer a far cheaper solution.

Once the design has been developed it will be possible to assign some realistic costs. To draw conclusions at this stage is conjecture or at best an educated guess. I'm not saying that guess work doesn't have its place but when refining the accuracy of the costs it is always a good idea to acknowledge the deficiencies of the estimate. If once a developed design has been costed it does not provide a healthy RoI then I would simply leave it at that, either way I will have learned a lot from the journey. My research has so far lead to several interesting fields of design and research that I wouldn't have reached in my usual walk of life, i.e., artificial coral reef, submarine / ship, bridge, tunnelling, anchorages, tidal systems, wave energy / prediction, ocean currents, hydropower, ocean floor topography.

Inventors need wide horizons, it is only from a unique perspective that original ideas are born.
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 28/10/2011 16:29:59
....You can dream on. The laws of physics and economics are still going to be there when you wake up.
the pulleys are not just a source of friction, but pointless. If you have not worked out why then I don't think you are going to get much further with this...

I thought we had got to the bottom of the 'laws of physics' - are you still questioning my claims?
..../snipped
Inventors need wide horizons, it is only from a unique perspective that original ideas are born.

Unfortunately Peter your idea has run into 3 forum posters - one a research scientist, one an engineer. and one a businessman; and all have criticised your idea from multiple angles and I believe concluded from their own knowledge and the information posted that your idea is fatally flawed.  Scientifically; the energy is limited, regardless of how much gearing or pulleys the energy available is limited by the volume of the pontoon and the size of the tide (a point I am not sure you grasp).  In Engineering terms this project is huge - the largest displacement of any floating object ever, dragging an object the size of a block of flats to the sea bed every 12 hours, as much wiring as the millennium dome, and all for 16MWh/day.  And Economically, with the best will in the world, with zero maintenance and running costs, and with unheard of efficiencies - you might start breaking even sometime in the 23rd century.  A hard-nosed analysis from three independent views cannot see the worth in this project
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 28/10/2011 17:06:21
A big strong non-floaty thing.
But the fish are smiling so it must be OK.

It doubles as an artificial reef, and, as you can see, fish like them.

Actually, it does not need to be very strong at all. It's pressurised so that it only needs to handle the variation in air pressure caused by the variation in head, which is not much at all (unfortunately). It could even be a flexible air bag of sorts. One big problem is securing the thing to the seabed.

I have to agree that it's probably not much use for a large power generation scheme, but it might be interesting for small scale generation on remote islands or similar where the cost of bringing in power is already prohibitive.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 28/10/2011 17:58:44
"I thought we had got to the bottom of the 'laws of physics' - are you still questioning my claims?"
There are two ways your idea could be made to work.
Make it vastly cheaper or get much more energy from it.
I was covering both bases.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 28/10/2011 22:30:20
Mootle,

I agree with BC and Matt about the viability and practicality of your approach. From a practicality standpoint alone, even if you could overcome the many issues that have been raised, keeping all that "kit" functioning in a highly corrosive submerged environment would be horribly expensive.

On the other hand, it is an intersting problem to try to solve. Here's another suggestion. It may not address viability, but it might address some of the practicalities. I'm sure BC and Matt will be more than delighted to point out any flaws it might have.


 [ Invalid Attachment ]

Basically, it consists of a pontoon attached to a (an?) hydraulic ram. The piston in the ram is attached to the seabed by a substantial cable. A high pressure hose connects the ram to a hydraulic motor (not shown) that could be used to do a lot of different things. The motor could sit on top of the pontoon, or on land, whichever is more convenient. The ram is filled with some sort of environmentally friendly liquid lubricant - vegetable oil perhaps?

As the tide rises, the force on the piston increases, and this drives the motor. (The fluid could also be prevented from escaping so that the energy can be tapped at a later point during the incoming tide.) When the tide falls again, the ram is refilled with liquid so that it's ready for the next cycle. The refilling does not consume much energy because it only has to lift the mass of the piston and cable against gravity.

To size the thing, we'd decide on the maximum hydraulic pressure in the hose between the ram and the motor first. If we decided that was 3000 psia, it tells us (I think!) that the volumetric ratio between the pontoon and the ram is around 3000/15, or 200:1 (that should be the equivalent of the pulley ratio in a mechanical version).

Although 3000 psia is highish, it's not all that high either. We might go up to around 12000 psia if it was worth it (the motor technology might get a bit exotic, but it would get us to an 800:1 ratio, which ain't too shabby).

That ratio would mean that every 1000 litres of pontoon displacement would require a whopping 1.25 litres of ram displacement.

However, even if this were to work in practice, it can't do anything to alter the fact that the available energy is determined by the displacement of the pontoon and tidal variation. Consequently, even if you can reduce the cost of the energy extraction system to zero, the cost of the pontoon is going to determine the viability of the system as a whole.

EDIT: Astute members of the forum will have already noted that the maximum possible travel of the piston in the ram should, ideally, be at least as great as the tidal variation.

EDIT2: I wonder how this stacks up against wind power? I do know that the economics of wind power are (to put it politely) a wee bit dodgy, and the aesthetic impact of wind power can be really horrible. The last time I was in Scotland, I was pretty disgusted by the desecration I observed. 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 29/10/2011 10:29:24
Unfortunately Peter your idea has run into 3 forum posters - one a research scientist, one an engineer. and one a businessman; and all have criticised your idea from multiple angles and I believe concluded from their own knowledge and the information posted that your idea is fatally flawed.

Interesting. The question posted was will this buoyancy engine work. In summary and disregarding areas of speculation the response was that the principle is sound and that the claimed energy balance and potential revenue stream is theoretically possible.


Scientifically; the energy is limited, regardless of how much gearing or pulleys the energy available is limited by the volume of the pontoon and the size of the tide (a point I am not sure you grasp).

Agreed, the tidal range and pontoon are the main constraints of the energy balance. I have no idea what gave you the impression that I do not understand this basic premise. 


In Engineering terms this project is huge - the largest displacement of any floating object ever, dragging an object the size of a block of flats to the sea bed every 12 hours, as much wiring as the millennium dome, and all for 16MWh/day.


Agreed, it is a big project, much bigger than you have indicated once it is scaled up. There are no easy rides with renewables, nothing comes for free.


And Economically, with the best will in the world, with zero maintenance and running costs, and with unheard of efficiencies - you might start breaking even sometime in the 23rd century.  A hard-nosed analysis from three independent views cannot see the worth in this project

It is too soon for me to draw any conclusions as to the economic viability. That can only come once there is more data to put into the business case. The schematic animation is only intended to get the principle across. Unfortunately, I'm not ready to answer the question on financial viability until the design has been sufficiently developed.

Once again, all input is appreciated - many thanks.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 29/10/2011 10:44:12
"I thought we had got to the bottom of the 'laws of physics' - are you still questioning my claims?"
There are two ways your idea could be made to work.
Make it vastly cheaper or get much more energy from it.
I was covering both bases.

OK, we have established that the laws of thermodynamics haven't been violated.

I agree with your summation. The initial line of development will be put the pontoon to work by combining, wind, solar & hydro to greatly increase the energy mix and yield. Zero fossil fuel, Hydrogen and fresh water production is also an option. Either way the engineering would be geared to give a desirable RoI before being presented to prospective investors.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 29/10/2011 11:13:31
EDIT2: I wonder how this stacks up against wind power? I do know that the economics of wind power are (to put it politely) a wee bit dodgy, and the aesthetic impact of wind power can be really horrible. The last time I was in Scotland, I was pretty disgusted by the desecration I observed. 

I don't think you would get a meaningful patent for your idea as it touches on other ideas which are already out there and even if it didn't you would have scuppered it by posting it on an public forum. As per the PM I sent to you, I think it would be a really useful service to offer a private forum where inventors could seek guidance / help with patenting / modelling and presentation from forum members. This would involve nondisclosure contracts being agreed between inventors and contributors. Once priority was in place the idea could then be discussed in an open forum to help refine the idea.

It's not a good idea to publically post any idea without first securing priority with a patent application.

Wind power is a multibillion pound industry. One of the reasons for this is that current legislation guarantees that investors get a good RoI over time. Large, offshore wind projects generate a lot of energy over time and will form an integral part of any renewable energy mix for a island such as the UK.

Hydropower tends to be used as a top up for peak periods of demand owing to the storage element. As the energy mix moves toward renewables the renewable mix reliability will become more important.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 29/10/2011 13:25:14
"In summary and disregarding areas of speculation the response was that the principle is sound and that the claimed energy balance and."
I don't agree that the " potential revenue stream is theoretically possible".
The revenue is small.
Whatever you make the structure from it will need to be maintained and repaired.
I think that the ongoing costs will exceed the revenue.
The only way it could conceivably work would be if we voted in a government who really wanted to waste money backing this scheme in spite of the fact that it will never produce as good a rate of return (KWH/£) as, for example, a wind turbine.
To get this to work you need to go into politics in a big way.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 29/10/2011 16:04:51
"You seem to be confusing revenue with cost."
No, since I said "costs will exceed the revenue" there's no way I could have thought they were the same thing.

The difference is clear to me. One is money coming in and the other is money going out.
To be a success, the money coming in has to exceed the money going out.
I don't think your system will or can ever achieve that.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 29/10/2011 16:50:32
I don't agree that the " potential revenue stream is theoretically possible".

You say that but from your previous post the above quote is flawed. Once the energy generation potential is agreed, the stated revenue is also deemed to be agreed since the revenue is calculated directly from the energy that is generated.

As to the cost, at this point in time I would agree that your 'guess' is as good as mine. However, when writing business cases I prefer to work it out. If the answer turns out per your speculation I will be the first to admit that the idea doesn't hold water but for now I simply do not have an answer to that question as the design development has not taken place.

ps. I deleted my earlier post as I modified that by mistake rather than quoting yours.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 29/10/2011 17:11:02
I don't think you would get a meaningful patent for your idea as it touches on .........

Actually, I'm not interested in obtaining a patent for something like this. I was really only interested in seeing if it's possible to come up with something that might have a snowball's chance of actually working. The fact that there is something similar to this already wouldn't surprise me, because this is one of the few ways it's actually going to work. If there is anything novel about this idea (which I doubt), I'm quite happy that I've prevented anyone else from patenting it.

There is little point in obtaining a patent on an alternative method of doing something that offers no advantages over an existing method. Also, "kitchen sink" patents that attempt to combine all sorts of existing techniques are pretty much worthless because it's too easy to bypass their claims, whereas some of the best patents are those that overcome a problem that the prior art has failed to deal with.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 29/10/2011 20:30:52
I took a shot at an economy version.

 [ Invalid Attachment ]

This might help to address BC's concern that you need a big strong floaty thing, though it does still need to be big and floaty.

The hydraulic ram is now submerged and attached to the float and the anchor by cables or chains. The big floaty thing is full of air under enough pressure to prevent it collapsing at that depth. Not shown in much detail (cos I was too lazy to draw it) is a net-like thing that surrounds the spherical float and spreads the load from the ram over its upper surface. Maybe that's made of Kevlar, or carbon fibre?

Exactly what the float is made of is a bit of a mystery. I suspect it could be from any number of things. The important thing is that the air must not be able to leak out quickly, although a small amount of leakage could be tolerated and made up from a supply of compressed air.

Obviously the ram should be enclosed to keep seawater away from it, particularly the rod.

Interestingly, the control system is remarkably simple. All it has to do is keep the hydraulic pressure in the ram at a minimum pressure. If the tide is rising, the pressure tends to rise, so the system sends fluid to the hydraulic motor to relieve the pressure. When the tide if falling, the system pumps fluid into the ram to maintain the minimum pressure. That ensures the float maintains a constant level relative to the water surface.
 


Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 30/10/2011 10:15:04
Mootle,
The biggest (by far) uncertainty in the revenue is some theoretical subsidy that a government might pay.
You seem to think the revenue stream is adequate.
I don't.
The numbers (uncertain though they are) are on my side.
It wasn't going to make money, even with a stupidly large subsidy.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 30/10/2011 11:09:02
Mootle,
The biggest (by far) uncertainty in the revenue is some theoretical subsidy that a government might pay.
You seem to think the revenue stream is adequate.
I don't.
The numbers (uncertain though they are) are on my side.
It wasn't going to make money, even with a stupidly large subsidy.

What ever you think, the government incentives are extant - if you are a citizen of the UK you're already paying for the policy to which Tony Blair committed the UK to many years ago. Energy suppliers are required to include a mix of renewables as part of their portfolio in order to retain their licence to operate.

It is absurd to assert that the numbers fall on either side. Math doesn't subscribe to favouritism, the numbers will be what they are, when the time comes - further dialogue in this regard is futile.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 30/10/2011 13:20:31
"What ever you think, the government incentives are extant - if you are a citizen of the UK you're already paying for the policy to which Tony Blair committed the UK to many years ago."
I'm a UK citizen. I'm aware of the analogous subsidy for some forms of renewable energy.
I'm also aware that the original planned subsidy is due to come to an end.
The current government is not enthusiastic about spending money (in general) so I wouldn't like to build a business case on the current subsidy.

On one side we have a cost measured inn tens or hundreds of millions. On the other we have a reliable revenue measured in hundreds of thousands per year.
The numbers on one side really are bigger than those on the other.
The side of the argument they favour is clearly the side that says "This is silly and will never work in a month of Sundays".
As far as I can tell, that's my side, not yours.

I know the suppliers are required to use renewables.
But they are not stupid.
I can go into town and pay £150 for a 50W wind turbine. so, with no economies of scale or government subsidy I can get power for £3 per W.
http://www.maplin.co.uk/50w-telescopic-vertical-axis-wind-turbine-396269
Your system produced something like 0.8MW ( ignoring efficiencies)
I could get that from 16000 similar wind turbines (it would be a stupid way to do it, but I could). That would cost me £2.4M
Or I could spend something like 10 or 100 times more on untested technology.
How stupid would I have to be to do that?



Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 30/10/2011 13:40:43
"What ever you think, the government incentives are extant - if you are a citizen of the UK you're already paying for the policy to which Tony Blair committed the UK to many years ago."
I'm a UK citizen. I'm aware of the analogous subsidy for some forms of renewable energy.
I'm also aware that the original planned subsidy is due to come to an end.
The current government is not enthusiastic about spending money (in general) so I wouldn't like to build a business case on the current subsidy.

On one side we have a cost measured inn tens or hundreds of millions. On the other we have a reliable revenue measured in hundreds of thousands per year.
The numbers on one side really are bigger than those on the other.
The side of the argument they favour is clearly the side that says "This is silly and will never work in a month of Sundays".
As far as I can tell, that's my side, not yours.

I know the suppliers are required to use renewables.
But they are not stupid.
I can go into town and pay £150 for a 50W wind turbine. so, with no economies of scale or government subsidy I can get power for £3 per W.
http://www.maplin.co.uk/50w-telescopic-vertical-axis-wind-turbine-396269
Your system produced something like 0.8MW ( ignoring efficiencies)
I could get that from 16000 similar wind turbines (it would be a stupid way to do it, but I could). That would cost me £2.4M
Or I could spend something like 10 or 100 times more on untested technology.
How stupid would I have to be to do that?

More speculation, a sizable chunk of nonesense and another serving of sarcasm but the fact remains that only time will tell.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 30/10/2011 15:11:42
The power generation rates are not speculative.
The price of the wind turbines are not speculative.
The only speculation and nonsense are your strange idea that your system will somehow become vastly cheaper than it is.
Time has, for all practical purposes, already told.
You (almost certainly) can't make one vital component of your system for the money it would cost to set up a known system.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 30/10/2011 19:07:42
I was quite encouraged by the "economy version", so I thought it might actually be useful in remote locations if it wasn't too expensive. I started with the assumption that I wanted to power a single 13A 230V outlet on Muckle Flugga - not continuously mind you - only while the tide was coming in at its maximum rate.

Assumptions:
The tide is rising at 0.15 mm/s.
Overall conversion efficiency to electricity is 60%

So,
Work is being done by rising tide at 4.6kJ/s
Force on ram is 4600/0.00015 = 30MN
Displacement of float is 30/10 = 3 Mega kg or 3000 tonnes.

The large floaty thing still needs to displace the equivalent of 1.5 million two litre soda bottles, and the anchor better weigh about 6000 tonnes.

Unless I mucked something up here (which is highly possible) this scheme is Le canard mort.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 30/10/2011 19:41:51
You might get an Arts Council grant to cover the cost.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 30/10/2011 19:51:19
The power generation rates are not speculative.

What seasonal efficiency do you think your turbine will achieve. A quick google of micro wind turbines will tell you that your own gut feeling for making such a comparison was indeed 'stupid'.

The price of the wind turbines are not speculative.

What do you think the installed cost of your turbine would be?

The only speculation and nonsense are your strange idea that your system will somehow become vastly cheaper than it is.


I haven't developed the design as yet, let alone costed it so how can it become vastly cheaper. I've set out why the the reused value of 7 large tankers is not a useful representation of the cost of the pontoon. Do you honestly think that repeating the same argument changes anything?


Time has, for all practical purposes, already told.
You (almost certainly) can't make one vital component of your system for the money it would cost to set
up a known system.

Only time will tell what shape the system design takes and thereafter the cost.

Only time will tell what revenue can be achieved by adopting a power mix.

Only time will tell what changes are made to the extant government incentive schemes.

You refusal to accept these basic premises are baffling.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 30/10/2011 20:35:21
I was quite encouraged by the "economy version", so I thought it might actually be useful in remote locations if it wasn't too expensive. I started with the assumption that I wanted to power a single 13A 230V outlet on Muckle Flugga - not continuously mind you - only while the tide was coming in at its maximum rate.

Assumptions:
The tide is rising at 0.15 mm/s.
Overall conversion efficiency to electricity is 60%

So,
Work is being done by rising tide at 4.6kJ/s
Force on ram is 4600/0.00015 = 30MN
Displacement of float is 30/10 = 3 Mega kg or 3000 tonnes.

The large floaty thing still needs to displace the equivalent of 1.5 million two litre soda bottles, and the anchor better weigh about 6000 tonnes.

Unless I mucked something up here (which is highly possible) this scheme is Le canard mort.

Your system wasn't fully defined so I've run a rough order calculation for a continuous 3kW demand.

For this purpose we would need (2) buoyancy engines.

Each system would require storage for 12hrs and a flow rate of ca. 0.0071m3/s.

A generator inlet CSA of 0.017m2 would give the flow rate based on a working head of 50m assuming an 85% turbine / generator efficiency.

Thus, the required Storage Vessel volume would be ca. 300m3, say a cylindrical tank ca. 10m diam * 4m.

Based on a 25:1 gearing ratio each Pontoon volume would be ca. 7,500m3, say equivalent to a rectangular tank ca. 65 * 20 * 6m.

Generation phases would be offset assuming a typical (2) tide per day cycle. Based on this arrangement the Pontoon loading would not occur simultaneously. Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.

Tidal range is assumed as 2m.

I don't plan to use a traditional anchor. 

This system is not optimised for revenue recovery but rather to meet a continuous demand in the absence of any energy mix.

No allowance has been made for gross volume.

If a continuous power supply isn't required I expect an hybrid solar PV / wind system would be a more cost effective solution for this particular application.

However, if it's important that your pc and lights continue to operate during the night time you might want to consider the Buoyancy Engine.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 30/10/2011 21:10:21
"What seasonal efficiency do you think your turbine will achieve. A quick google of micro wind turbines will tell you that your own gut feeling for making such a comparison was indeed 'stupid'."
Yes, But I did it on purpose.
I deliberately chose a ridiculous system and I ignored obvious  factors like the fact that you wouldn't use such small generators and also that you would qualify for a bulk discount. I also ignored the fact that these things only run when the wind blows. Of course, the importance of that depends on where you put them. Where I live the mean wind speed isn't high enough to turn that generator.

However, in spite of all that - which as you say makes them stupid.
The purchase cost is still less than your idea. Not marginally less, not a bit less, but a whole lot less. Something like £2.4M rather than tens or hundreds of millions. You keep saying that time will tell what the true cost will be. Fair enough, but can you (as I have asked before) come up with some explanation of why you feel that you will be able to make this cheaper than, for example, a scarp supertanker?


Incidentally, you say
"I don't plan to use a traditional anchor. "
presumably that means you plan to use something more expensive or you think that the professionals have been getting it wrong all this time.

Your idea that the government will suddenly decide to fund your dead duck rather than, for example this live one is the baffling thing
http://en.wikipedia.org/wiki/Salter's_duck

The government thinks renewable power is a good thing. So do I, but that's not the point.
So they will fund schemes to generate it.
But they won't fund any old scheme. They schemes have to compete against each other.
Since there's no way that you can build yours for less than roughly 10 times the cost of a bunch of stupidly inefficient ones which deliver the same power, there's no incentive for them to fund it.
You will always make a loss on this.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 30/10/2011 22:00:41
Your system wasn't fully defined so I've run a rough order calculation for a continuous 3kW demand.

I encourage you to scrutinize my numbers very carefully. Either I mucked them up, or you are stiffing yourself by making the pontoons twice as large as they need to be.

As I mentioned a couple of times already, and as any engineer worth their salt will point out, it's generally a really good idea to figure out how much energy is actually going into a system so that we can compare and contrast it with the amount of energy that is coming out of the system. When we figure it all out, net energy should be pretty close to zero.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 30/10/2011 23:40:59
You might get an Arts Council grant to cover the cost.


Strangely enough, I did consider that possibility.

My application to the Arts Council includes a twenty meter bust of Julius Geezer made from crushed beer cans that sits atop the big floaty thing. The residents of Muckle Flugga are bound to appreciate it.

I have named my artistic endeavour "Roman in the Gloamin"
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 01/11/2011 19:36:16
"What seasonal efficiency do you think your turbine will achieve. A quick google of micro wind turbines will tell you that your own gut feeling for making such a comparison was indeed 'stupid'."
Yes, But I did it on purpose.
I deliberately chose a ridiculous system and I ignored obvious  factors like the fact that you wouldn't use such small generators and also that you would qualify for a bulk discount. I also ignored the fact that these things only run when the wind blows. Of course, the importance of that depends on where you put them. Where I live the mean wind speed isn't high enough to turn that generator.

However, in spite of all that - which as you say makes them stupid.
The purchase cost is still less than your idea. Not marginally less, not a bit less, but a whole lot less. Something like £2.4M rather than tens or hundreds of millions. You keep saying that time will tell what the true cost will be. Fair enough, but can you (as I have asked before) come up with some explanation of why you feel that you will be able to make this cheaper than, for example, a scarp supertanker?


Incidentally, you say
"I don't plan to use a traditional anchor. "
presumably that means you plan to use something more expensive or you think that the professionals have been getting it wrong all this time.

Your idea that the government will suddenly decide to fund your dead duck rather than, for example this live one is the baffling thing
http://en.wikipedia.org/wiki/Salter's_duck

The government thinks renewable power is a good thing. So do I, but that's not the point.
So they will fund schemes to generate it.
But they won't fund any old scheme. They schemes have to compete against each other.
Since there's no way that you can build yours for less than roughly 10 times the cost of a bunch of stupidly inefficient ones which deliver the same power, there's no incentive for them to fund it.
You will always make a loss on this.

You really don't get this at all. Whilst it is interesting to get 'points of view' it does get a little tiresome going over the same points. Suffice to say I will use meaningful data for the business case rather than ill informed guess work. I don't see that this should be such an affront to your sensibilities, after all I've made no claims as to the system costs to date.

Despite, what you think this is a new idea so anchorage for such a development would need an innovative approach. Typically, the loading is compressive rather than tensile and the forces involved will be huge. As I indicated previously, I will show the principles on a construction animation once I get around to it. My objective is to attain healthy savings against traditional marine anchorage methods whilst improving the sustainability of such a scheme.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 01/11/2011 20:00:13
Your system wasn't fully defined so I've run a rough order calculation for a continuous 3kW demand.

I encourage you to scrutinize my numbers very carefully. Either I mucked them up, or you are stiffing yourself by making the pontoons twice as large as they need to be.

As I mentioned a couple of times already, and as any engineer worth their salt will point out, it's generally a really good idea to figure out how much energy is actually going into a system so that we can compare and contrast it with the amount of energy that is coming out of the system. When we figure it all out, net energy should be pretty close to zero.

As I indicated your system wasn't fully defined.

I find it better to start with a generator rating, this is used to establish the Storage Volume, once the generation time is determined. Then comes the Pontoon sizing based on the selected gearing ratio.

I've done a rough and ready estimate based on a system which will produce 3kW continuously. Our system efficiency may vary but otherwise I would expect the figures to work out. This increases the Storage Vessel volume which will in turn increase the Pontoon volume.

Since you didn't define the operating time I thought this was preferable to second guessing what you've allowed for although in broad terms, for a 3,000m3 Pontoon a matched Storage Vessel of 120m3 @ 25:1 gearing would be estimated as little over 4 1/2hrs of generation for your stated load.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 01/11/2011 20:44:37
I find it better to start with a generator rating, this is used to establish the Storage Volume, once the generation time is determined. Then comes the Pontoon sizing based on the selected gearing ratio.

Yes, but it looks as if you are basing the storage volume based on the way you believe your invention ought to work. If you don't determine the energy supplied by the tide directly, you have no means of cross checking your answer. It's not as if it's difficult to determine the energy input either.

I simply determined the power input by the maximum tidal rate (which, admittedly, I did sort of noodle) and derated it according to a efficiency factor. My calculation pays absolutely no attention to gear ratios etc. because they are completely irrelevant.

More specifically;

Power input x efficiency = power output.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 01/11/2011 21:01:39
I find it better to start with a generator rating, this is used to establish the Storage Volume, once the generation time is determined. Then comes the Pontoon sizing based on the selected gearing ratio.

Yes, but it looks as if you are basing the storage volume based on the way you believe your invention ought to work. If you don't determine the energy supplied by the tide directly, you have no means of cross checking your answer. It's not as if it's difficult to determine the energy input either.

I simply determined the power input by the maximum tidal rate (which, admittedly, I did sort of noodle) and derated it according to a efficiency factor. My calculation pays absolutely no attention to gear ratios etc. because they are completely irrelevant.

More specifically;

Power input x efficiency = power output.

It has been demonstrated that all things being equal and accounting for efficiency it really doesn't matter which way you work out the energy balance.

Generator work done = Pontoon work done = Storage Vessel work done.

I'd rather hoped that we had moved on from the energy balance. From a economy of scale perspective this scheme doesn't make sense for the buoyancy engine but I would agree that it is useful to look at the small scale as it can sometimes help to quantify matters. 
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 01/11/2011 21:02:13
The payback time of this project will certainly be longer than the lifetime of a government.
The only way it could work is with government backing (because it produces electricity that's a lot more expensive than the current wholesale rate).
So, when you say "Suffice to say I will use meaningful data for the business case rather than ill informed guess work. " all you can mean is that you will use your guess of what government subsidy will be available, rather than my guess.

Fair enough, but don't pretend it's anything but a guess.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 01/11/2011 21:12:37
The payback time of this project will certainly be longer than the lifetime of a government.
The only way it could work is with government backing (because it produces electricity that's a lot more expensive than the current wholesale rate).
So, when you say "Suffice to say I will use meaningful data for the business case rather than ill informed guess work. " all you can mean is that you will use your guess of what government subsidy will be available, rather than my guess.

Fair enough, but don't pretend it's anything but a guess.

I'm not pretending anything. When writing a business case the revenue is calculated based on the extant government incentives.

It is true that the FIT scheme is under review and as such that uncertainty would have to be declared. However, would you not agree that if the Buoyancy Engine was set to work today, the given revenue figures would be achievable according to the rough order energy balance that has been agreed?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 01/11/2011 21:30:46

Generator work done = Pontoon work done = Storage Vessel work done.



IMHO, that's a dangerous way to look at it, and it can easiliy lead to confusion, QED.

It should be;

Tide work done = all lost energy + captured energy.

The tide is the source of the energy, not the pontoon.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 01/11/2011 22:03:02

Generator work done = Pontoon work done = Storage Vessel work done.



IMHO, that's a dangerous way to look at it, and it can easiliy lead to confusion, QED.

It should be;

Tide work done = all lost energy + captured energy.

The tide is the source of the energy, not the pontoon.

You're leaning against an open door here - my point is that it works out all ways around, the only question mark relates to the system efficiency. Turbines and generators can work very efficiently if correctly matched to the application and this should be the main input for a well designed system. It is more difficult to establish the overall system efficiency. This will be a function of the the pulley system, the additional buoyancy needed to drive the ascent phase, allowances for coral growth etc, trimming losses (governing swell,) cable stretch, Pontoon sinkage, down time for maintenance / unsuitable operating conditions.... 
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 01/11/2011 22:11:33
"would you not agree that if the Buoyancy Engine was set to work today, the given revenue figures would be achievable according to the rough order energy balance that has been agreed?"
My deliberately absurdly high estimate of the combined tariffs and subsidies was the equivalent of 4 times the actual value of the electricity produced.
I think your figures came out at something like half that figure.
It doesn't matter because, as I pointed out, many times,

Unless you can show how you are suddenly going to make this scheme a lot cheaper, it will never "break even" because the guessed revenues will never exceed the cost of paying the interest on the capital investment.

Worse, even if you could make it break even, it would still be a couple of orders of magnitude more expensive that just buying an absurdly expensive system.

I have asked the same question plenty of times and you don't seem to understand the importance of it.
How are you going to make your system ten times cheaper than the scrap value of the pontoon?


Oh, BTW, I write, and review business cases for the government.

We do take account of the fact that the plug might get pulled and, if that looks likely, we simply don't support the work. We don't do work that is likely to depend on long term support because that's not a good use of the investor's capital. So that's "When writing a business case the revenue is calculated based on the extant government incentives." scuppered.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 02/11/2011 04:53:44

Generator work done = Pontoon work done = Storage Vessel work done.



IMHO, that's a dangerous way to look at it, and it can easiliy lead to confusion, QED.

It should be;

Tide work done = all lost energy + captured energy.

The tide is the source of the energy, not the pontoon.

You're leaning against an open door here - my point is that it works out all ways around, the only question mark relates to the system efficiency. Turbines and generators can work very efficiently if correctly matched to the application and this should be the main input for a well designed system. It is more difficult to establish the overall system efficiency. This will be a function of the the pulley system, the additional buoyancy needed to drive the ascent phase, allowances for coral growth etc, trimming losses (governing swell,) cable stretch, Pontoon sinkage, down time for maintenance / unsuitable operating conditions.... 

Your pontoons are capable of producing 588.6MJ in 24 hours which means your efficiency is 44.1%

How does that strike you?

Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 05/11/2011 09:06:35

Generator work done = Pontoon work done = Storage Vessel work done.



IMHO, that's a dangerous way to look at it, and it can easiliy lead to confusion, QED.

It should be;

Tide work done = all lost energy + captured energy.

The tide is the source of the energy, not the pontoon.

You're leaning against an open door here - my point is that it works out all ways around, the only question mark relates to the system efficiency. Turbines and generators can work very efficiently if correctly matched to the application and this should be the main input for a well designed system. It is more difficult to establish the overall system efficiency. This will be a function of the the pulley system, the additional buoyancy needed to drive the ascent phase, allowances for coral growth etc, trimming losses (governing swell,) cable stretch, Pontoon sinkage, down time for maintenance / unsuitable operating conditions.... 

Your pontoons are capable of producing 588.6MJ in 24 hours which means your efficiency is 44.1%

How does that strike you?


Without trying to second guess your calculations did you take into account my comment:

'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 05/11/2011 09:21:43
"would you not agree that if the Buoyancy Engine was set to work today, the given revenue figures would be achievable according to the rough order energy balance that has been agreed?"
My deliberately absurdly high estimate of the combined tariffs and subsidies was the equivalent of 4 times the actual value of the electricity produced.
I think your figures came out at something like half that figure.
It doesn't matter because, as I pointed out, many times,

Unless you can show how you are suddenly going to make this scheme a lot cheaper, it will never "break even" because the guessed revenues will never exceed the cost of paying the interest on the capital investment.

Worse, even if you could make it break even, it would still be a couple of orders of magnitude more expensive that just buying an absurdly expensive system.

I have asked the same question plenty of times and you don't seem to understand the importance of it.
How are you going to make your system ten times cheaper than the scrap value of the pontoon?


Oh, BTW, I write, and review business cases for the government.

We do take account of the fact that the plug might get pulled and, if that looks likely, we simply don't support the work. We don't do work that is likely to depend on long term support because that's not a good use of the investor's capital. So that's "When writing a business case the revenue is calculated based on the extant government incentives." scuppered.

You are presupposing which way the future FIT scheme will go. I've already indicated that the current uncertainty would need to be declared:
 
'It is true that the FIT scheme is under review and as such that uncertainty would have to be declared.'

Your difficulty comes from not being able to distinguish points of view from fact. The fact is no costing claims have been made. I've set out why I don't think the assumptions made are reliable. For now I will press on with the scaled model animation, after which reasonably accurate costs can be established.

We seem to be going around in circles so unless anyone has some new questions I declare myself out of the thread for the time being.

Once again, thanks to all that took the time to comment.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 05/11/2011 14:21:39
This isn't a POV, it's a fact.
I can get the same nominal electricity generating potential as your machine for something like £2.4M

It's also renewable power, so it would presumably get the same FIT. (Granted that is a POV, but I think it's a reasonable one.)
So, unless you can build your scheme for less than that sum your system isn't financially viable.

It's also a fact that your rig needs a big pontoon.
It's a reasonable POV to say that it's in many ways similar to a ship. The stresses on it are different, but comparable (actually they are probably more difficult to manage).

It's not an unreasonable POV that shipbuilders know what they are doing.
They use steel so it's fair to say that steel is a good material to use in terms of cost versus practicality.
SO it's not unreasonable to conclude tat your system, which is quite like a ship, will have a cost comparable with a ship of the same displacement.

I have asked several times what you could do to make it significantly cheaper than a ship of that size. You don't seem to have offered any answer to that.
So, it seems that you must agree that the cost estimate is not absurdly wrong.

However that means that, if someone built your system they could sell it for the scrap value.
That value is rather more than £2.4M. Probably one or two orders of magnitude more.
So they could sell it for scrap, buy the wind turbines, sell the same power back to the grid for the same  money and pocket a huge sum of money.

Let me know which of my assumptions you feel is actually unreasonable, rather than just pointing out that they are assumptions. I know they are not cast in stone, but the point is that they only need to be very roughly correct to show that your system will fail to cover its cost.

Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 06/11/2011 01:29:43

Generator work done = Pontoon work done = Storage Vessel work done.



IMHO, that's a dangerous way to look at it, and it can easiliy lead to confusion, QED.

It should be;

Tide work done = all lost energy + captured energy.

The tide is the source of the energy, not the pontoon.

You're leaning against an open door here - my point is that it works out all ways around, the only question mark relates to the system efficiency. Turbines and generators can work very efficiently if correctly matched to the application and this should be the main input for a well designed system. It is more difficult to establish the overall system efficiency. This will be a function of the the pulley system, the additional buoyancy needed to drive the ascent phase, allowances for coral growth etc, trimming losses (governing swell,) cable stretch, Pontoon sinkage, down time for maintenance / unsuitable operating conditions.... 

Your pontoons are capable of producing 588.6MJ in 24 hours which means your efficiency is 44.1%

How does that strike you?


Without trying to second guess your calculations did you take into account my comment:

'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'


Yes, I did. As you didn't specify its displacement, I assumed it was twice the displacement of the two smaller ones. If you knew it was possible to generate the power output with half the total displacement, I would have thought you would have made that clear.

My calculation was simply the energy output over the maximum energy input based on the displacements and the tide.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 06/11/2011 18:39:59
This isn't a POV, it's a fact.
I can get the same nominal electricity generating potential as your machine for something like £2.4M

It's also renewable power, so it would presumably get the same FIT. (Granted that is a POV, but I think it's a reasonable one.)
So, unless you can build your scheme for less than that sum your system isn't financially viable.

It's also a fact that your rig needs a big pontoon.
It's a reasonable POV to say that it's in many ways similar to a ship. The stresses on it are different, but comparable (actually they are probably more difficult to manage).

It's not an unreasonable POV that shipbuilders know what they are doing.
They use steel so it's fair to say that steel is a good material to use in terms of cost versus practicality.
SO it's not unreasonable to conclude tat your system, which is quite like a ship, will have a cost comparable with a ship of the same displacement.

I have asked several times what you could do to make it significantly cheaper than a ship of that size. You don't seem to have offered any answer to that.
So, it seems that you must agree that the cost estimate is not absurdly wrong.

However that means that, if someone built your system they could sell it for the scrap value.
That value is rather more than £2.4M. Probably one or two orders of magnitude more.
So they could sell it for scrap, buy the wind turbines, sell the same power back to the grid for the same  money and pocket a huge sum of money.

Let me know which of my assumptions you feel is actually unreasonable, rather than just pointing out that they are assumptions. I know they are not cast in stone, but the point is that they only need to be very roughly correct to show that your system will fail to cover its cost.

For the umpteenth time, I do not think it's a good idea to make an estimate until a design has been done. I have offered various answers to your questions that seem perfectly reasonable to me but you have chosen to disregard them.

I fail to see how you can offer up the comparison with any kind of seriousness. It is so flawed that it isn't worth consideration even if you did include things like installation and whether it could actually provide load when you need it.

Perhaps we should all purchase a domestic petrol powered generator rather than invest in our energy infrastructure since those power stations would probably represent poor value for money by comparison. 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 06/11/2011 18:50:33
Yes, I did. As you didn't specify its displacement, I assumed it was twice the displacement of the two smaller ones. If you knew it was possible to generate the power output with half the total displacement, I would have thought you would have made that clear.

My calculation was simply the energy output over the maximum energy input based on the displacements and the tide.

I thought I did (3rd time lucky):
'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'

If you show your workings I can review further. The problem I have is that even when you are presented with irrefutable evidence you still don't concede points so I have no intention of trying to second guess what you have calculated.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 06/11/2011 19:47:53
Yes, I did. As you didn't specify its displacement, I assumed it was twice the displacement of the two smaller ones. If you knew it was possible to generate the power output with half the total displacement, I would have thought you would have made that clear.

My calculation was simply the energy output over the maximum energy input based on the displacements and the tide.

I thought I did (3rd time lucky):
'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'

If you show your workings I can review further. The problem I have is that even when you are presented with irrefutable evidence you still don't concede points so I have no intention of trying to second guess what you have calculated.

OK - here you go.

Quote
Based on a 25:1 gearing ratio each Pontoon volume would be ca. 7,500m3
Tidal range is assumed as 2m.

Total displacement 2 x 7500 = 15,000m3, or 15,000,000kg (ignoring the salt in the water)
Therefore, max force is 147.2MN
Max work in 24 hours is 147.2 x 4 = 588.6MJ = 588,600kJ
Max work per second is 588,600/86,400 = 6.81kJ
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%

(Or are you assuming one of the pontoons is going to spring a leak and sink?)
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 06/11/2011 20:58:43
OK, so I first asked "What developments would you put on your "wish list" that would actually make your system anything other than a white elephant?"
here
http://www.thenakedscientists.com/forum/index.php?topic=41578.msg370908#msg370908
Your reply was "there are various aspects of this application that we haven't touched on that would require development. "

So again I asked
"Clearly, to make your idea work there has to be a major change somewhere and that change has to make your system a lot cheaper.

What do you think can make it work?"
And I repeated essentially the same question
"It's still not going to work unless there's some magic change in the economics so I'd still like to see Mootle's answer to my question.
What can you change to make this idea work?"

And you said this
"As I've said before there are many developmental steps required.

I agree, steel prices are only likely to go up with time (as energy costs soar). This is one reason for aiming to minimise the use of steel in the system design.

One of the biggest challenges will be the anchorage. I don't think the use of large quantities of concrete will be sustainable or cost effective. I'm working on a construction animation to show the sequences involved and would post this in due course - house rules permitting"

So you say you won't use steel because it's expensive. It is however in practical terms quite cheap. That's why shipbuilders use it.

And you say you won't use concrete for the footings.
Good luck finding anything strong enough, heavy enough and cheaper than concrete.
So, thus far you have yet to really answer the question. YOu have made a couple of questionable comments about what you won't do (i.e. use steel or concrete), but nothing about what you will do.

This suggestion "I'm researching the possibility of reinforced plastics for the main base." was kicked into touch by Geezer when he pointed out that it's going to need to be very strong. Anyway I don't think reinforced plastics are much cheaper than steel if you actually need much strength.


And you don't seem to have addressed the issue of tying the pulleys down.
"Seriously, if they still use concrete for building things like the Thames Barrier, why do you think plastic might be better?
Do you think they are idiots?"

You don't seem to have replied to that. What you next said on the subject (unless I missed something was
"I've set out why the the reused value of 7 large tankers is not a useful representation of the cost of the pontoon. "
which is unfortunate since, so far as I can see, you didn't (though you did say you had deleted a post- perhaps it was there that you explained why your big strong floaty thing would be cheaper than someone else's design of big strong floaty thing.)

Again you say things like "I don't plan to use a traditional anchor. " without saying what you will use and ignoring the fact that traditional anchors wouldn't have got  to be traditional if they didn't work.

So, once again I asked " Fair enough, but can you (as I have asked before) come up with some explanation of why you feel that you will be able to make this cheaper than, for example, a scarp supertanker?"

And your reply was "Whilst it is interesting to get 'points of view' it does get a little tiresome going over the same points."
You don't seem to have understood that the way to avoid the tiresome repetition of a question is simply to answer it. Saying "this is a new idea so anchorage for such a development would need an innovative approach." doesn't actually tell us anything.

So, once again I asked
"How are you going to make your system ten times cheaper than the scrap value of the pontoon?"

And what do I get in reply?
I get this " I have offered various answers to your questions that seem perfectly reasonable to me but you have chosen to disregard them. "

Well, they may seem reasonable to you but from my point of view they seem to lack a fairly fundamental aspect.
You still haven't said what you are going to do to make this work for about 100 times less than the scrap value of the pontoon.

This is a science website.
People who put forward ideas are expected to answer questions asked about those ideas.

If I have missed an answer of the form "I will do (whatever) which is cheaper than using an old oil tanker" then please point it out to me
I'm not going to accept an answer that says "I haven't costed it yet" because that's the whole point; several of us have costed it and it's preposterously expensive.
I'm also not going to accept an answer that says "I will sprinkle magic pixie dust on the cost and make it go away" or, the roughly equivalent " I will need to do some research in reinforced plastics" or "I won't use a traditional anchor".

Now I challenge you to answer the question in a straightforward manner or leave.

How will you make this rig cheap enough that the revenue will, at least, service the loan for building it?









Title: Will this buoyancy engine-based generator work?
Post by: johan_M on 08/11/2011 20:43:01
Quote
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%
I have'nt followed the whole thread, it's a bit convoluted. Please explain this efficiency part?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 08/11/2011 21:15:08
Quote
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%
I have'nt followed the whole thread, it's a bit convoluted. Please explain this efficiency part?

Which part of it do you not understand?
Title: Will this buoyancy engine-based generator work?
Post by: damocles on 08/11/2011 23:19:20
Quote
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%
I have'nt followed the whole thread, it's a bit convoluted. Please explain this efficiency part?


Which part of it do you not understand?

Is it possible that the missing link is "efficiency = power out/power in" ?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 08/11/2011 23:57:38
Quote
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%
I have'nt followed the whole thread, it's a bit convoluted. Please explain this efficiency part?


Which part of it do you not understand?

Is it possible that the missing link is "efficiency = power out/power in" ?


It's actually a bit more complicated  [:D]

All the power never actually "went in". The system has the potential of acquiring a lot more energy from the tide than it outputs, so it's more a measure of volumetric, or displacement, efficiency.

The trouble with efficiencies is they can refer to lots of different measurements. If you ever want to start a really heated argument in a pub, efficiency is a good way to do it (it's usually a good idea to leave shortly after you start the argument [;D])
Title: Will this buoyancy engine-based generator work?
Post by: johan_M on 09/11/2011 00:41:49
What do you mean by displacement efficiency? Where does the lost energy go?can you give a simple example?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 09/11/2011 04:01:16
What do you mean by displacement efficiency? Where does the lost energy go?can you give a simple example?

There is no lost energy (well, there will be some due to parasitic losses like friction etc.) but this measurement is not about energy efficiency. We're evaluating the efficient use of the volume of the pontoon (which is a good thing to do because the pontoon is a very expensive part of the system.)

Based on the total possible energy in versus actual energy out, the pontoons might only be half the size (to displace the required amount of water), hence an efficiency of less than 50%. This also tells us that the pontoons are probably twice as expensive as they need to be.

The thing about efficiency is that it can refer to all sorts of things, not just energy.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 11/11/2011 20:26:17
Yes, I did. As you didn't specify its displacement, I assumed it was twice the displacement of the two smaller ones. If you knew it was possible to generate the power output with half the total displacement, I would have thought you would have made that clear.

My calculation was simply the energy output over the maximum energy input based on the displacements and the tide.

I thought I did (3rd time lucky):
'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'

If you show your workings I can review further. The problem I have is that even when you are presented with irrefutable evidence you still don't concede points so I have no intention of trying to second guess what you have calculated.

OK - here you go.

Quote
Based on a 25:1 gearing ratio each Pontoon volume would be ca. 7,500m3
Tidal range is assumed as 2m.

Total displacement 2 x 7500 = 15,000m3, or 15,000,000kg (ignoring the salt in the water)
Therefore, max force is 147.2MN
Max work in 24 hours is 147.2 x 4 = 588.6MJ = 588,600kJ
Max work per second is 588,600/86,400 = 6.81kJ
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%

(Or are you assuming one of the pontoons is going to spring a leak and sink?)

Ok, thanks for this. The idea that I was trying to get across was that (2) buoyancy engines working on this cycle would be able to share a single Pontoon owing to the sequencing of the loading of the Pontoon. This wouldn't be the optimum efficiency in terms of revenue generation for the system but it might be useful to suit certain demand profiles. The combined Pontoon would need to have an increased volume over (1) 7,500m3, maybe 10,000 - 12,000m3 would be possible with the main factor being distribution of stresses vs VfM. This would be subject to a detailed scaled design but since I haven't got the luxury of a design team behind me I will stick to the unitary system for now.

There are too many unknown variables at this point but I would anticipate that compared with other renewable energy systems the seasonal efficiency of a working system will be quite impressive.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 11/11/2011 20:38:42
Now I challenge you to answer the question in a straightforward manner or leave.

How will you make this rig cheap enough that the revenue will, at least, service the loan for building it?

As I've said (more than once,) I'm not ready to properly present and fully answer your question at this particular moment.

Once I've developed the Scaled and Construction Animation sufficiently I will return.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 12/11/2011 01:50:03
Yes, I did. As you didn't specify its displacement, I assumed it was twice the displacement of the two smaller ones. If you knew it was possible to generate the power output with half the total displacement, I would have thought you would have made that clear.

My calculation was simply the energy output over the maximum energy input based on the displacements and the tide.

I thought I did (3rd time lucky):
'Therefore, there is scope to engineer an arrangement such that both Storage Vessels operate from one Pontoon, which carries a number of operational and financial advantages.'

If you show your workings I can review further. The problem I have is that even when you are presented with irrefutable evidence you still don't concede points so I have no intention of trying to second guess what you have calculated.

OK - here you go.

Quote
Based on a 25:1 gearing ratio each Pontoon volume would be ca. 7,500m3
Tidal range is assumed as 2m.

Total displacement 2 x 7500 = 15,000m3, or 15,000,000kg (ignoring the salt in the water)
Therefore, max force is 147.2MN
Max work in 24 hours is 147.2 x 4 = 588.6MJ = 588,600kJ
Max work per second is 588,600/86,400 = 6.81kJ
Max power in = 6.81 kW
Power out = 3.0kw
Efficiency = 44.1%

(Or are you assuming one of the pontoons is going to spring a leak and sink?)

Ok, thanks for this. The idea that I was trying to get across was that (2) buoyancy engines working on this cycle would be able to share a single Pontoon owing to the sequencing of the loading of the Pontoon. This wouldn't be the optimum efficiency in terms of revenue generation for the system but it might be useful to suit certain demand profiles. The combined Pontoon would need to have an increased volume over (1) 7,500m3, maybe 10,000 - 12,000m3 would be possible with the main factor being distribution of stresses vs VfM. This would be subject to a detailed scaled design but since I haven't got the luxury of a design team behind me I will stick to the unitary system for now.

There are too many unknown variables at this point but I would anticipate that compared with other renewable energy systems the seasonal efficiency of a working system will be quite impressive.

Yes, I figured it was something like that.

BTW, I think you really need to worry about the 25:1 pulley speed up ratio. I'm pretty sure there will be so much friction that that pontoon will not be able to exert sufficient force on the storage vessel to move it.

In practice, even with a lot of anti-friction bearings (and super-flexible cable) I think you will discover there is no way around it. A small model of that part of the system might be a good investment.

An even cheaper method would be to get a 25:1 gear setup and try to run it in speed-up mode. If you have really good bearings, the output might actually rotate 25 times faster than the input under no load (although it's also possible the gears will strip before it turns at all), but as soon as you put any load on it, it will very likely wedge.   
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 12/11/2011 16:12:56
Now I challenge you to answer the question in a straightforward manner or leave.

How will you make this rig cheap enough that the revenue will, at least, service the loan for building it?

As I've said (more than once,) I'm not ready to properly present and fully answer your question at this particular moment.

Once I've developed the Scaled and Construction Animation sufficiently I will return.

An animation will not make it cheaper,
You could answer the question without that trouble.
You have mentioned a few things you will not do, but not what you will do instead.

I think you have absolutely no idea how you are going to make this idea economically viable.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 13/11/2011 10:57:16
Now I challenge you to answer the question in a straightforward manner or leave.

How will you make this rig cheap enough that the revenue will, at least, service the loan for building it?

As I've said (more than once,) I'm not ready to properly present and fully answer your question at this particular moment.

Once I've developed the Scaled and Construction Animation sufficiently I will return.

An animation will not make it cheaper,
You could answer the question without that trouble.
You have mentioned a few things you will not do, but not what you will do instead.

I think you have absolutely no idea how you are going to make this idea economically viable.

The idea of this thread was to see if the system would work in principle.

Your speculations as to what ideas are in my head are noted but as the authority in this respect I assure you that you are wrong. I'm aware of the difficult challenges but have a number of innovative solutions in mind. Exploring these lines takes time but until the design is fixed the cost of the system is nothing more than a known unknown. This thread has reinforced a need to improve the available revenue and I'm satisfied that with a sensible balance of technologies I will have a reasonable shot at value engineering a solution which provides a reasonable business case.

Once I've developed my theorem to a point at which I'm ready to present I will return if that's OK.

Thank you for your patience.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 13/11/2011 11:19:43
Yes, I figured it was something like that.

BTW, I think you really need to worry about the 25:1 pulley speed up ratio. I'm pretty sure there will be so much friction that that pontoon will not be able to exert sufficient force on the storage vessel to move it.

In practice, even with a lot of anti-friction bearings (and super-flexible cable) I think you will discover there is no way around it. A small model of that part of the system might be a good investment.

An even cheaper method would be to get a 25:1 gear setup and try to run it in speed-up mode. If you have really good bearings, the output might actually rotate 25 times faster than the input under no load (although it's also possible the gears will strip before it turns at all), but as soon as you put any load on it, it will very likely wedge.  

Pulley's are still my preferred option as I haven't worked out how to make a gearbox solution work for this application but I'm still mulling that one over.

I've recognised the need to maintain load and this would be achieved by not allowing the Storage Vessel to break the surface following the Ascent phase, as stated on the audio of the Schematic animation. However, I acknowledge this isn't what's shown so apologies for the misunderstanding.

I agree that a lower ratio would be easier from an engineering perspective. The 25:1 ratio is a target driven by revenue optimisation. A pilot scheme is the next step but before I would look for scheme funding I need to be sure that there is a business case. If I can demonstrate a business case I would look to enter into consultation with specialists for a number of elements of the design where I'm not a practitioner. The pulley system would be one such area.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 13/11/2011 23:52:45
Yes, I figured it was something like that.

BTW, I think you really need to worry about the 25:1 pulley speed up ratio. I'm pretty sure there will be so much friction that that pontoon will not be able to exert sufficient force on the storage vessel to move it.

In practice, even with a lot of anti-friction bearings (and super-flexible cable) I think you will discover there is no way around it. A small model of that part of the system might be a good investment.

An even cheaper method would be to get a 25:1 gear setup and try to run it in speed-up mode. If you have really good bearings, the output might actually rotate 25 times faster than the input under no load (although it's also possible the gears will strip before it turns at all), but as soon as you put any load on it, it will very likely wedge.  

Pulley's are still my preferred option as I haven't worked out how to make a gearbox solution work for this application but I'm still mulling that one over.

I've recognised the need to maintain load and this would be achieved by not allowing the Storage Vessel to break the surface following the Ascent phase, as stated on the audio of the Schematic animation. However, I acknowledge this isn't what's shown so apologies for the misunderstanding.

I agree that a lower ratio would be easier from an engineering perspective. The 25:1 ratio is a target driven by revenue optimisation. A pilot scheme is the next step but before I would look for scheme funding I need to be sure that there is a business case. If I can demonstrate a business case I would look to enter into consultation with specialists for a number of elements of the design where I'm not a practitioner. The pulley system would be one such area.

Er, well, you might want to take a squint at this before you go much further, particularly the term that shows that the efficiency is related to the inverse of a value raised to the power of the number of sheaves. 25:1 is going to need a lot of sheaves. 

http://en.wikipedia.org/wiki/Block_and_tackle#Friction
Title: Will this buoyancy engine-based generator work?
Post by: imatfaal on 14/11/2011 12:12:49
http://en.wikipedia.org/wiki/Block_and_tackle#Friction

My word there is something call a "luff tackle" - please don't tell sheepy

And wikipedia has gone weird and textbased
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 14/11/2011 19:12:29
Is that similar to wedding tackle?
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 14/11/2011 21:13:22
Yes, I figured it was something like that.

BTW, I think you really need to worry about the 25:1 pulley speed up ratio. I'm pretty sure there will be so much friction that that pontoon will not be able to exert sufficient force on the storage vessel to move it.

In practice, even with a lot of anti-friction bearings (and super-flexible cable) I think you will discover there is no way around it. A small model of that part of the system might be a good investment.

An even cheaper method would be to get a 25:1 gear setup and try to run it in speed-up mode. If you have really good bearings, the output might actually rotate 25 times faster than the input under no load (although it's also possible the gears will strip before it turns at all), but as soon as you put any load on it, it will very likely wedge.  

Pulley's are still my preferred option as I haven't worked out how to make a gearbox solution work for this application but I'm still mulling that one over.

I've recognised the need to maintain load and this would be achieved by not allowing the Storage Vessel to break the surface following the Ascent phase, as stated on the audio of the Schematic animation. However, I acknowledge this isn't what's shown so apologies for the misunderstanding.

I agree that a lower ratio would be easier from an engineering perspective. The 25:1 ratio is a target driven by revenue optimisation. A pilot scheme is the next step but before I would look for scheme funding I need to be sure that there is a business case. If I can demonstrate a business case I would look to enter into consultation with specialists for a number of elements of the design where I'm not a practitioner. The pulley system would be one such area.

Er, well, you might want to take a squint at this before you go much further, particularly the term that shows that the efficiency is related to the inverse of a value raised to the power of the number of sheaves. 25:1 is going to need a lot of sheaves. 

http://en.wikipedia.org/wiki/Block_and_tackle#Friction

I would refer you to my earlier comments on this topic but would add that the pulley system would be developed specifically for the application with high efficiency in mind. I expect that a clutch system coupled with a particular arrangement would be needed to help stabilise the Storage Vessel against the effects of swell etc.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 15/11/2011 07:05:54
"I would refer you to my earlier comments on this topic but would add that the pulley system would be developed specifically for the application with high efficiency in mind."
Do you think the previous pulley systems were designed to be inefficient?
Don't forget that you also have to make it cheaper than the traditional ones.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 15/11/2011 08:21:22
Do you think the previous pulley systems were designed to be inefficient?

Now look here! If it was good enough for the Romans, it's good enough for us.

You'll be trying to tell us you can replace it with some ridiculous hydraulic system next.
Title: Will this buoyancy engine-based generator work?
Post by: johan_M on 15/11/2011 20:34:59
Mootle,
 You are not going to convince BoredChemist and Geezer with any amount of software emulation. You won't convince the rest of us either. You won't even convince yourself.
 You need to roll up your sleeves and build a small scale model. Get yourself a large tub, valves, pulleys etc.Build your pontoon and storage vessels from plastic containers.
Get a small gearbox from RS components and small separately exited dc motor as well.Then build a generator.
Get a small smart relay to do the logic and timing to control the valves and emulate the tides.
 It's not difficult or expensive to do.
 At least you'll then try to prove your basic concept.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 15/11/2011 21:59:45
To be honest, I'm not going to be convinced by a scale model.
I have no doubt the system could be built (on a small or large scale).
I just don't think it will ever be built cheaply enough to be any use.
Title: Will this buoyancy engine-based generator work?
Post by: johan_M on 16/11/2011 00:01:01
Quote
To be honest, I'm not going to be convinced by a scale model.
I have no doubt the system could be built (on a small or large scale).
I just don't think it will ever be built cheaply enough to be any use
He has to prove he CAN generate power first, by overcoming all the engineering problems. It must be simple and efficient. IF he achieve this ( a big if ), then he might raise money to build another small model off shore. Then he could scale the costs and prove that his system has a chance. 
  If he is convinced, then he has to get working on it.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 16/11/2011 03:29:40
He has to prove he CAN generate power first, by overcoming all the engineering problems. It must be simple and efficient. IF he achieve this ( a big if ), then he might raise money to build another small model off shore. Then he could scale the costs and prove that his system has a chance. 
  If he is convinced, then he has to get working on it.

I don't think there is any doubt that some sort of pontoon arrangement can generate power from the tide. The version Mootle proposes is not likely to for a variety of reasons, but some very conventional hydraulics could easily overcome most of those problems.

But that's not the issue. The recovered energy is very small in relation to the size (and therefore cost) of the pontoons. That's not a problem that can be solved by any amount of engineering. It's simply a matter of basic physics. If seawater was ten times denser than it is, or if the tide rose ten time higher than it does, things might be different.

EDIT: We might get some idea of the scale if we could answer this;

Gasoline (aka petrol) contains about 44MJ/kg (million joules of energy per kilogram).

How many kilograms of seawater would a tide have to lift to increase the potential energy of the seawater by 44 MJ, or how high would a tide have to elevate one kilogram of seawater to increase its potential energy by 44MJ?

That's probably a bit unfair, because work can be extracted from elevated water quite efficiently, so, assume gasoline only has an energy density of 10MJ/kg.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 17/11/2011 17:51:53
Quote
To be honest, I'm not going to be convinced by a scale model.
I have no doubt the system could be built (on a small or large scale).
I just don't think it will ever be built cheaply enough to be any use
He has to prove he CAN generate power first, by overcoming all the engineering problems. It must be simple and efficient. IF he achieve this ( a big if ), then he might raise money to build another small model off shore. Then he could scale the costs and prove that his system has a chance. 
  If he is convinced, then he has to get working on it.

Thanks for this.

Bored Chemist is correct, there is no doubt that electricity could be generated as the principles of hydropower are well known but the cost is the key to the business case.

This is no chore for me as I enjoy the design process, even if it doesn't work out I will still have learned from the process. Suffice to say the lines of enquiry I'm working on are nothing like the suggested tanker in respect to the structure or materials used for the Pontoon.

The scaled animation will help to inform the cost and thus the viability of the business case. Providing the business case is viable I would then seek funding for a small pilot scheme.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 17/11/2011 18:10:18
I don't think there is any doubt that some sort of pontoon arrangement can generate power from the tide. The version Mootle proposes is not likely to for a variety of reasons, but some very conventional hydraulics could easily overcome most of those problems.

But that's not the issue. The recovered energy is very small in relation to the size (and therefore cost) of the pontoons. That's not a problem that can be solved by any amount of engineering. It's simply a matter of basic physics. If seawater was ten times denser than it is, or if the tide rose ten time higher than it does, things might be different.

I think your conclusions are a little premature. But here are some video's that follow tidal and wave themes using hydraulics and compressed air that you've proposed.

I would maintain that the Buoyancy Engine has potential for large scale power generation but some of the other ideas may also have their place.

http://www.youtube.com/watch?v=av2Uf_AvDIA&feature=player_embedded (http://www.youtube.com/watch?v=av2Uf_AvDIA&feature=player_embedded)
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 17/11/2011 18:55:40
Tidal power works.
There are several ways to implement it
http://en.wikipedia.org/wiki/Tidal_power
But I don't see Mootle's system ever being manufactured cheaply enough to be commercially viable.
Title: Will this buoyancy engine-based generator work?
Post by: JP on 17/11/2011 21:57:53
Interesting.  All the techniques basically involve building a dam or putting a generator in the water to harness the flow of water horizontally past it rather than the tidal rise. 

You could fill an inlet with pontoons to harness the energy, but you could get roughly the same amount of energy by damming the inlet off and harnessing the energy as the water flows into and out of the inlet due to the tides.  Obviously for a sizable inlet, its cheaper to build a dam than fill it entirely with pontoons. 
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 18/11/2011 00:25:29
Interesting.  All the techniques basically involve building a dam or putting a generator in the water to harness the flow of water horizontally past it rather than the tidal rise. 

You could fill an inlet with pontoons to harness the energy, but you could get roughly the same amount of energy by damming the inlet off and harnessing the energy as the water flows into and out of the inlet due to the tides.  Obviously for a sizable inlet, its cheaper to build a dam than fill it entirely with pontoons. 

Right - it's a shame really because tidal energy is very dependable, unlike wind and solar energy. Unfortunately, the energy density in the elevated seawater is very small, so you have to deal with gigantic quantities of the stuff to produce a decent amount of power, and that might have a serious impact on the environment.

Still, for some isolated locations where you need a limited amount of dependable power, a small-scale pontoon type generator might be the way to go.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 20/11/2011 18:15:05
Interesting.  All the techniques basically involve building a dam or putting a generator in the water to harness the flow of water horizontally past it rather than the tidal rise. 

You could fill an inlet with pontoons to harness the energy, but you could get roughly the same amount of energy by damming the inlet off and harnessing the energy as the water flows into and out of the inlet due to the tides.  Obviously for a sizable inlet, its cheaper to build a dam than fill it entirely with pontoons. 

Right - it's a shame really because tidal energy is very dependable, unlike wind and solar energy. Unfortunately, the energy density in the elevated seawater is very small, so you have to deal with gigantic quantities of the stuff to produce a decent amount of power, and that might have a serious impact on the environment.

Still, for some isolated locations where you need a limited amount of dependable power, a small-scale pontoon type generator might be the way to go.

Actually, massive amounts of power can be generated (even more so with greater depth,) but with the Buoyancy Engine as the power is increased the generating period reduces.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 20/11/2011 18:38:08
OK, but the average power is determined by the size of the floats and the tidal range.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 20/11/2011 19:33:15
Actually, massive amounts of power can be generated (even more so with greater depth,) but with the Buoyancy Engine as the power is increased the generating period reduces.

Sure, as long as you are talking about instantaneous power. In terms of energy, the maximum energy output is limited by the displacement of the pontoon(s).
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 20/11/2011 20:18:58
Actually, massive amounts of power can be generated (even more so with greater depth,) but with the Buoyancy Engine as the power is increased the generating period reduces.

Sure, as long as you are talking about instantaneous power. In terms of energy, the maximum energy output is limited by the displacement of the pontoon(s).

I don't think average power or instantaneous power tell the full storey for power generation technologies such as this. It takes a wider view of the national grid and its frailties.

In terms of power generation there are various system arrangements that can be geared to certain applications, i.e., a few minutes of massive power output might be very useful for some scientific experiments or more typically a high power output for a few hours might be necessary to maintain services during peak demand.

For optimum ROI it is better to select a more modest power rating to meet a base load.

It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 20/11/2011 20:50:49
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 20/11/2011 21:05:25
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.
Title: Will this buoyancy engine-based generator work?
Post by: damocles on 20/11/2011 21:37:09
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

Mootle that would not be a fair comparison because it would assume a 100% energy conversion in your yet-to-be-designed "pulley system". I have no engineering background, but previous posts in this thread suggest that the energy conversion in any pulley system with a 25:1 upgearing would be lucky to reach 5%. The fair comparison would be water with a 2.5 m head perhaps?
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 20/11/2011 22:18:46
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

OK,
if the depth is 50M the pressure is about 5bar or 500,000 Pa
Each cubic metre of stored"space" at that depth represents 500KJ of energy.
A common way to store energy is to use a flywheel so lets use that as a comparator.
A disk made from steel 1 metre in diameter and 14 cm or so thick would have a mass of a tonne- the same as a cubic metre of water (near enough).
That gives a moment of inertia (I) of 0.5*1000*.5*.5 =125 (I think the units are kg m^2)

The stored energy would  be 1/2 I (omega)^2
500,000=62.5 (omega) ^2
So, to store the same energy as a cubic metre of tank i.e. 500 KJ, the angular velocity would have to be 89 radians per second.
If I have the maths right it only needs to do about 850 RPM to store the same energy and it doesn't need a set of pulleys and ropes.
Flywheels used for energy storage are generally spun a lot faster than that.
So, compared to a simple flywheel, your system isn't very good.

Actually, it might be easy to make it a lot better.
Any generator that is expected to deliver very high peak power will have a lot of thick wires and a lot of iron in the rotor. All that metal will have a lot of mass, and it will be rotating.
So, rather than messing about with pontoons and tanks, you might be able to use the generator itself as a flywheel (it's a fairly common technique for getting high peak powers) and use much cheaper electricity from the mains to spin it up (many generators can be run "in reverse" as motors.

Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 21/11/2011 02:12:06
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

I hope I don't have to refer you to Homer Simpson again!

Forget the gears, pulleys and all other paraphernalia. We are talking about the energy density of the seawater which is the only source of energy input to the system.

Let's say the tide rises 2m every tide. That means the potential energy of each kg of water elevated by the tide has increased by

1 x 9.81 x 2 = 19.62kJ

There are two tides in 24 hours, so the potential energy per kilogram of water has increased by a whopping 39.24kJ in 24 hours.

By comparison, 1kg of gasoline has an energy density of 44.4MJ. That's only a bit more that 1000 times greater.

You can mess around with gears, pulleys, cranks, hydraulics and levers till the cows come home, but you can never alter the fact that the energy density of the water elevated by the tide is very small (unless you can make tides rise and fall a lot further, or significantly alter the density of seawater.)

 
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 21/11/2011 07:11:52
I don't think he's trying to rewrite thermodynamics, energy is conserved, but power isn't and you could store the tidal energy harvested and then let it out in a rush to produce a high peak power.
It's possible, but pointless because there are better ways to do this(not to mention that the efficiency will drop due to bigger viscous losses in the pipes.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 21/11/2011 08:19:14
I don't think he's trying to rewrite thermodynamics, energy is conserved, but power isn't and you could store the tidal energy harvested and then let it out in a rush to produce a high peak power.
It's possible, but pointless because there are better ways to do this(not to mention that the efficiency will drop due to bigger viscous losses in the pipes.

Yes you could do that, but the energy density of seawater elevated by the tide is still very small which is why tidal systems need to harness very large volumes of seawater to produce much useful energy.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 21/11/2011 18:40:41
It's possible, but pointless because there are better ways to do this(not to mention that the efficiency will drop due to bigger viscous losses in the pipes.

I'm more concerned it won't even get that far. When the tide rises there is a distinct possibility that the pontoon won't even budge because of the friction in the pulley system. 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/11/2011 20:01:45
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

I hope I don't have to refer you to Homer Simpson again!

Forget the gears, pulleys and all other paraphernalia. We are talking about the energy density of the seawater which is the only source of energy input to the system.

Let's say the tide rises 2m every tide. That means the potential energy of each kg of water elevated by the tide has increased by

1 x 9.81 x 2 = 19.62kJ

There are two tides in 24 hours, so the potential energy per kilogram of water has increased by a whopping 39.24kJ in 24 hours.

By comparison, 1kg of gasoline has an energy density of 44.4MJ. That's only a bit more that 1000 times greater.

You can mess around with gears, pulleys, cranks, hydraulics and levers till the cows come home, but you can never alter the fact that the energy density of the water elevated by the tide is very small (unless you can make tides rise and fall a lot further, or significantly alter the density of seawater.)

Since it is the sea water at depth which would act upon turbine / generator set it is more in keeping with convention to refer to this as the working fluid. You must recalculate based on this in order to perform a fair comparison.
 
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/11/2011 20:27:03
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

Mootle that would not be a fair comparison because it would assume a 100% energy conversion in your yet-to-be-designed "pulley system". I have no engineering background, but previous posts in this thread suggest that the energy conversion in any pulley system with a 25:1 upgearing would be lucky to reach 5%. The fair comparison would be water with a 2.5 m head perhaps?

A well engineered 25:1 pulley system could achieve high efficiency although it is appreciated that it is easier to achieve high efficiency with lower pulley gearing ratio's. Value engineering and consultation with experts in that field would inform the built solution.

In any case the energy density of the working fluid is unaffected by the pulley ratio. For instance a 5:1 ratio would simply take 5 tidal cycles to achieve the target depth instead of 1 based on 25:1. Thus, the gearing ratio is only considered when calculating the energy availability. Many surface tidal energy systems do suffer from low energy density and this would constrain their eligibility for large scale power generation but this system does not fall into that category.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/11/2011 20:40:32
Interesting.  All the techniques basically involve building a dam or putting a generator in the water to harness the flow of water horizontally past it rather than the tidal rise. 

You could fill an inlet with pontoons to harness the energy, but you could get roughly the same amount of energy by damming the inlet off and harnessing the energy as the water flows into and out of the inlet due to the tides.  Obviously for a sizable inlet, its cheaper to build a dam than fill it entirely with pontoons. 

Dams are actually quite costly as you can see from a quick Google. I would estimate building a large pontoon is much cheaper. Of course that is only one part of the equation. Most things have a cost and storing energy is no exception. Most viable locations in the UK have been taken and countries with more viable locations tend to make full use of them. This is because hydropower is very useful.

Think of the Buoyancy Engine as a portable dam.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 21/11/2011 21:35:15
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

OK,
if the depth is 50M the pressure is about 5bar or 500,000 Pa
Each cubic metre of stored"space" at that depth represents 500KJ of energy.
A common way to store energy is to use a flywheel so lets use that as a comparator.
A disk made from steel 1 metre in diameter and 14 cm or so thick would have a mass of a tonne- the same as a cubic metre of water (near enough).
That gives a moment of inertia (I) of 0.5*1000*.5*.5 =125 (I think the units are kg m^2)

The stored energy would  be 1/2 I (omega)^2
500,000=62.5 (omega) ^2
So, to store the same energy as a cubic metre of tank i.e. 500 KJ, the angular velocity would have to be 89 radians per second.
If I have the maths right it only needs to do about 850 RPM to store the same energy and it doesn't need a set of pulleys and ropes.
Flywheels used for energy storage are generally spun a lot faster than that.
So, compared to a simple flywheel, your system isn't very good.

Actually, it might be easy to make it a lot better.
Any generator that is expected to deliver very high peak power will have a lot of thick wires and a lot of iron in the rotor. All that metal will have a lot of mass, and it will be rotating.
So, rather than messing about with pontoons and tanks, you might be able to use the generator itself as a flywheel (it's a fairly common technique for getting high peak powers) and use much cheaper electricity from the mains to spin it up (many generators can be run "in reverse" as motors.

I really don't think you understand how the renewable energy sector works but let's indulge your notion and ignore the finite nature of the primary energy sources used for a typical grid power generation.

As stated, more than once, I haven't indicated a cost yet because the design is under development but let's consider the cost of the main alternatives:

A nuclear power station requires a Uranium mining site, Uranium refining plant, nuclear power plant,  containment, disposal etc... 

or perhaps you prefer a fossil fuel alternative so we would have...

The fact is energy generation isn't cheap, none of the methods work without taking a long term investment approach even before we get into renewable technologies. Feel free to develop your flywheel idea but if it's all the same to you I'll persue my idea for the time being.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/11/2011 03:54:07
It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

I hope I don't have to refer you to Homer Simpson again!

Forget the gears, pulleys and all other paraphernalia. We are talking about the energy density of the seawater which is the only source of energy input to the system.

Let's say the tide rises 2m every tide. That means the potential energy of each kg of water elevated by the tide has increased by

1 x 9.81 x 2 = 19.62kJ

There are two tides in 24 hours, so the potential energy per kilogram of water has increased by a whopping 39.24kJ in 24 hours.

By comparison, 1kg of gasoline has an energy density of 44.4MJ. That's only a bit more that 1000 times greater.

You can mess around with gears, pulleys, cranks, hydraulics and levers till the cows come home, but you can never alter the fact that the energy density of the water elevated by the tide is very small (unless you can make tides rise and fall a lot further, or significantly alter the density of seawater.)

Since it is the sea water at depth which would act upon turbine / generator set it is more in keeping with convention to refer to this as the working fluid. You must recalculate based on this in order to perform a fair comparison.
 

I really think you're missing something here.

The source of the energy is the tide elevating the mass of water displaced by the pontoon. Regardless of how you convert that energy into a more useful form, and even if the conversion system has zero losses, you cannot ever get more energy out than the tide put in.

The energy density of the water is very relevant because it tells you the absolute maximum energy input for any displacement.

If you know the overall efficiency of your conversion system, you can easily determine the energy output by multiplying the mass of water displaced by its energy density, then multiplying that by the overall efficiency. At the very least, it's a good way of checking to see if your other calculations are valid.

What is the design target for the overall efficiency of your conversion system?

Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/11/2011 04:35:42

A well engineered 25:1 pulley system could achieve high efficiency although it is appreciated that it is easier to achieve high efficiency with lower pulley gearing ratio's. Value engineering and consultation with experts in that field would inform the built solution.


Why don't you just run the numbers? You should be able to find out pretty quickly if your needs are at least feasible with available anti-friction bearing technology. If you discover you are are off by a factor of ten, consultants probably won't be able to help much.

For your application you are going to need roller bearings that can support large radial loads. You won't be able to find anything better for reducing friction under heavy loads.

Here's a link to SKF. If they can't meet your needs, I doubt if there is any other technology available that can. You'll find a calculator here that will compute the friction at a pulley.
 
http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_4_1
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 22/11/2011 07:16:39
"I really don't think you understand how the renewable energy sector works but let's indulge your notion and ignore the finite nature of the primary energy sources used for a typical grid power generation. "
I thought that you had moved on from the idea that this was a useful source of renewable energy and were touting it as a pulse power system.
I was pointing out that it fails in that role too.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/11/2011 18:49:48
I really think you're missing something here.

The source of the energy is the tide elevating the mass of water displaced by the pontoon. Regardless of how you convert that energy into a more useful form, and even if the conversion system has zero losses, you cannot ever get more energy out than the tide put in.

The energy density of the water is very relevant because it tells you the absolute maximum energy input for any displacement.

If you know the overall efficiency of your conversion system, you can easily determine the energy output by multiplying the mass of water displaced by its energy density, then multiplying that by the overall efficiency. At the very least, it's a good way of checking to see if your other calculations are valid.

What is the design target for the overall efficiency of your conversion system?

If you want to depart from convention that's up to you but it's not good practice or a fair representation for this application.

It would be too subjective to provide substantiation at this stage but I would anticipate the overall system efficiency to be ca. 50% +/- 20%.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/11/2011 19:18:18

A well engineered 25:1 pulley system could achieve high efficiency although it is appreciated that it is easier to achieve high efficiency with lower pulley gearing ratio's. Value engineering and consultation with experts in that field would inform the built solution.


Why don't you just run the numbers? You should be able to find out pretty quickly if your needs are at least feasible with available anti-friction bearing technology. If you discover you are are off by a factor of ten, consultants probably won't be able to help much.

For your application you are going to need roller bearings that can support large radial loads. You won't be able to find anything better for reducing friction under heavy loads.

Here's a link to SKF. If they can't meet your needs, I doubt if there is any other technology available that can. You'll find a calculator here that will compute the friction at a pulley.
 
http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_4_1

Thanks for this, I'm familiar with SKF and have used their products for a number of automotive / industrial applications. There is such a wide array of options available, but this would not be a standard application and would certainly be an area for specialist input.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/11/2011 19:25:37
"I really don't think you understand how the renewable energy sector works but let's indulge your notion and ignore the finite nature of the primary energy sources used for a typical grid power generation. "
I thought that you had moved on from the idea that this was a useful source of renewable energy and were touting it as a pulse power system.
I was pointing out that it fails in that role too.

Now there you go again, claiming to know what's in my mind which are completely apposed to my representations here.

Suffice to say, and not for the first time, you are in error.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/11/2011 19:36:27
If you want to depart from convention that's up to you but it's not good practice or a fair representation for this application.

Oh, so when you buy a car presumably you do find out how far it actually might go on a liter of fuel, or would that be too unconventional?

It would be too subjective to provide substantiation at this stage but I would anticipate the overall system efficiency to be ca. 50% +/- 20%.

That's a gigantic swing. Did you actually compute this range?

A well engineered 25:1 pulley system could achieve high efficiency

What's your source for this subjective statement? According to the information I posted it's going to be extremely inefficient.

You do realize that a well engineered 25:1 pulley system might well prevent the pontoon from producing any energy at all. Have you actually done any calculations to try to determine the friction in the pulley system?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/11/2011 19:51:53

A well engineered 25:1 pulley system could achieve high efficiency although it is appreciated that it is easier to achieve high efficiency with lower pulley gearing ratio's. Value engineering and consultation with experts in that field would inform the built solution.


Why don't you just run the numbers? You should be able to find out pretty quickly if your needs are at least feasible with available anti-friction bearing technology. If you discover you are are off by a factor of ten, consultants probably won't be able to help much.

For your application you are going to need roller bearings that can support large radial loads. You won't be able to find anything better for reducing friction under heavy loads.

Here's a link to SKF. If they can't meet your needs, I doubt if there is any other technology available that can. You'll find a calculator here that will compute the friction at a pulley.
 
http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_4_1

Thanks for this, I'm familiar with SKF and have used their products for a number of automotive / industrial applications. There is such a wide array of options available, but this would not be a standard application and would certainly be an area for specialist input.

There's nothing fancy about it (other than keeping the seawater out of the bearings.) Each pulley requires a bearing, or set of bearings, that can handle the radial load. To get a good approximation, you don't need to worry about axial load, and speed is unlikely to be an issue.

All you need to know are the coefficients of static and dynamic friction for a rolling bearing (which are remarkably small and you should be able to find them at SKF, or phone them up) then you can determine the amount of friction if you know the load. Next step is to plug the data into the block-and-tackle formula and you should get a pretty good idea.

Didn't you do something similar to this before you filed the patent?
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 22/11/2011 20:11:25
If you want to depart from convention that's up to you but it's not good practice or a fair representation for this application.

Oh, so when you buy a car presumably you do find out how far it actually might go on a liter of fuel, or would that be too unconventional?

It would be too subjective to provide substantiation at this stage but I would anticipate the overall system efficiency to be ca. 50% +/- 20%.

That's a gigantic swing. Did you actually compute this range?

A well engineered 25:1 pulley system could achieve high efficiency

What's your source for this subjective statement? According to the information I posted it's going to be extremely inefficient.

You do realize that a well engineered 25:1 pulley system might well prevent the pontoon from producing any energy at all. Have you actually done any calculations to try to determine the friction in the pulley system?

Taking your questions in order:

No, I'm referring to the conventional use of 'working fluid'.

Not really, I think this level of accuracy is appropriate at such an early stage in the design process.

I'm basing my statement on experience of low friction applications. It is all very well paraphrasing but in fairness I have already indicated the typical factors involved.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 22/11/2011 20:33:08
No, I'm referring to the conventional use of 'working fluid'.

Obviously - it's like designing a car where you only pay attention to the transmission and ignore the engine bit  [:D]. The "engine bit" is the pontoon and pulley system. The overal system efficiency has to take that into account (although you may not want to know that.)

Quote
Not really, I think this level of accuracy is appropriate at such an early stage in the design process.

It's not a question of accuracy. It's a question of viability. The viability model has to assume the worst case prediction. You did base your model on the worst case I hope?

Quote
I'm basing my statement on experience of low friction applications. It is all very well paraphrasing but in fairness I have already indicated the typical factors involved.

Then you don't need consultants because you already have a pretty good idea how efficient the pulley system is. What did your calculation predict?
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 22/11/2011 20:36:36
This

Interesting.  All the techniques basically involve building a dam or putting a generator in the water to harness the flow of water horizontally past it rather than the tidal rise. 

You could fill an inlet with pontoons to harness the energy, but you could get roughly the same amount of energy by damming the inlet off and harnessing the energy as the water flows into and out of the inlet due to the tides.  Obviously for a sizable inlet, its cheaper to build a dam than fill it entirely with pontoons. 

Right - it's a shame really because tidal energy is very dependable, unlike wind and solar energy. Unfortunately, the energy density in the elevated seawater is very small, so you have to deal with gigantic quantities of the stuff to produce a decent amount of power, and that might have a serious impact on the environment.

Still, for some isolated locations where you need a limited amount of dependable power, a small-scale pontoon type generator might be the way to go.

Actually, massive amounts of power can be generated (even more so with greater depth,) but with the Buoyancy Engine as the power is increased the generating period reduces.

is Mootle saying the system can generate high peak power

And this

Actually, massive amounts of power can be generated (even more so with greater depth,) but with the Buoyancy Engine as the power is increased the generating period reduces.

Sure, as long as you are talking about instantaneous power. In terms of energy, the maximum energy output is limited by the displacement of the pontoon(s).

I don't think average power or instantaneous power tell the full storey for power generation technologies such as this. It takes a wider view of the national grid and its frailties.

In terms of power generation there are various system arrangements that can be geared to certain applications, i.e., a few minutes of massive power output might be very useful for some scientific experiments or more typically a high power output for a few hours might be necessary to maintain services during peak demand.

For optimum ROI it is better to select a more modest power rating to meet a base load.

It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.


is where he says it's useful

So I don't think it was unreasonable for me to think he was talking about the merit of this sytem being that it can produce high peak power which is useful in some circumstances.
I just pointed out there are much easier and cheaper ways to do it.

So I think this
"I really don't think you understand how the renewable energy sector works but let's indulge your notion and ignore the finite nature of the primary energy sources used for a typical grid power generation. "
I thought that you had moved on from the idea that this was a useful source of renewable energy and were touting it as a pulse power system.
I was pointing out that it fails in that role too.

Now there you go again, claiming to know what's in my mind which are completely apposed to my representations here.

Suffice to say, and not for the first time, you are in error.

is more than a little ironic.
In particular in speculating that I don't know about renewables (even though, as I have said, it's part of my job) he has done pretty much what he accused me of  (the  bit about "Now there you go again, claiming to know what's in my mind ") and turned it into an ad hom attack.
Title: Will this buoyancy engine-based generator work?
Post by: damocles on 23/11/2011 00:45:58
There is a real hidden agenda here!

The thread was started with the title "Will this buoyancy engine-based generator work?"
There has been a really clear and resounding "no!" from half a dozen contributors (in the form of 'unlikely to work', and 'ridiculously uneconomical even if it does') <my paraphrase; I am not quoting anyone in particular>. In the course of the thread, the original poster has shifted ground several times about the real purpose of the device (Energy generation? Energy storage? Peak load dumping?), doing whatever it takes to defend his pet project. The contributors who have persisted in the debate all have some expertise, quite significant in some cases.

-- If the OP really wanted an answer to the question, why use this forum rather than approach a real expert -- engineering professor at a university, for example, to preserve commercial neutrality.
-- Insofar as he was looking for an answer here, at this stage he has it. Further debate is not likely to change the opinions of those who have been posting; rather, positions appear to have solidified.

The defence itself often appears quite illogical. For example in the reply to my post

It is true that the buoyancy of the Pontoon is one of constraints but I thought your comment on energy density was also a little misleading. The energy is effectively stored in the Storage Vessel (SV) and once the SV has reached the desired depth the energy density can be considerable.

There was nothing misleading about my statement. The source of the energy is the potential energy increase in the mass of water, and that is simply a function of the change in height and the mass. The energy density is very small.

The energy can be recovered in different ways, but you can never overcome the limitation imposed by the low energy density of the elevated water, and that fundamental limitation applies to all tidal energy systems.

I disagree since this system involves a pulley system.

I would be interested to see a few examples of your energy density comparison based on sea water with a 50m head.

Mootle that would not be a fair comparison because it would assume a 100% energy conversion in your yet-to-be-designed "pulley system". I have no engineering background, but previous posts in this thread suggest that the energy conversion in any pulley system with a 25:1 upgearing would be lucky to reach 5%. The fair comparison would be water with a 2.5 m head perhaps?

A well engineered 25:1 pulley system could achieve high efficiency although it is appreciated that it is easier to achieve high efficiency with lower pulley gearing ratio's. Value engineering and consultation with experts in that field would inform the built solution.

In any case the energy density of the working fluid is unaffected by the pulley ratio. For instance a 5:1 ratio would simply take 5 tidal cycles to achieve the target depth instead of 1 based on 25:1. Thus, the gearing ratio is only considered when calculating the energy availability. Many surface tidal energy systems do suffer from low energy density and this would constrain their eligibility for large scale power generation but this system does not fall into that category.

If the gearing ratio is so irrelevant and a 5:1 could be used equally as well, why not ask for a comparison with a 10 m head of water? Or why not talk about a 500 m head of water for comparison based on a 250:1 gearing system, and then point out the irrelevance of the gearing ratio? Something is greatly amiss with the logic!
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 23/11/2011 06:58:51
Not only has the logic been strained and the goalposts mobile, but there has been a persistent refusal to even consider the cost, and therefore the fact that this is too expensive to work.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/11/2011 19:25:46
No, I'm referring to the conventional use of 'working fluid'.

Obviously - it's like designing a car where you only pay attention to the transmission and ignore the engine bit  [:D]. The "engine bit" is the pontoon and pulley system. The overal system efficiency has to take that into account (although you may not want to know that.)

Quote
Not really, I think this level of accuracy is appropriate at such an early stage in the design process.

It's not a question of accuracy. It's a question of viability. The viability model has to assume the worst case prediction. You did base your model on the worst case I hope?

Quote
I'm basing my statement on experience of low friction applications. It is all very well paraphrasing but in fairness I have already indicated the typical factors involved.

Then you don't need consultants because you already have a pretty good idea how efficient the pulley system is. What did your calculation predict?

Taking your questions in order:

I didn't define the term 'working fluid' this is simply the recognised meaning.

Actually your question was to do with efficiency. Since this is very much a work in progress which is why I indicated rough order accuracy.

I have no idea how you would reach that conclusion based upon my responses.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 24/11/2011 19:43:00
If the gearing ratio is so irrelevant and a 5:1 could be used equally as well, why not ask for a comparison with a 10 m head of water? Or why not talk about a 500 m head of water for comparison based on a 250:1 gearing system, and then point out the irrelevance of the gearing ratio? Something is greatly amiss with the logic!

Let's set a few things straight:

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.

When discussing average energy the gearing ratio is a significant factor.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 24/11/2011 20:19:29
"When discussing average energy the gearing ratio is a significant factor."
No.
Just plain wrong.
The energy (average or otherwise) is the product of the force applied by the float to its rope and the distance it pulls that rope.

The energy is fixed by the size of the pontoon and the tidal range.

All the gearing can do is make things worse- right down to the point where the pulleys seize and the work done is zero.
They could do that with a 1:1 ratio or a 1:1000 ratio.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/11/2011 01:52:17

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.
 

In terms of thermodynamics the gear ratio is everything to do with the energy density of the working fluid in the turbine. It's the gear ratio that determines the energy density of the working fluid in the turbine by multiplying the tidal head by the gear ratio to produce the turbine head.

If you are only interested in the relationship between the turbine and the working fluid in the turbine you are confusing fluid dynamics with thermodynamics.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/11/2011 21:33:14
"When discussing average energy the gearing ratio is a significant factor."
No.
Just plain wrong.
The energy (average or otherwise) is the product of the force applied by the float to its rope and the distance it pulls that rope.

The energy is fixed by the size of the pontoon and the tidal range.

All the gearing can do is make things worse- right down to the point where the pulleys seize and the work done is zero.
They could do that with a 1:1 ratio or a 1:1000 ratio.

I'm not sure you're following the thread at all since much of this has already been covered more than once. Of course the energy is fixed by the size of the pontoon but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

The rating (power output during generation,) is determined by finding a suitable static head whilst the generating duration is found from the flow rate through the turbine and storage volume of the Storage Vessel. For the scaled animation the static head is 50m. Thus, in simple terms to achieve the optimum energy output we aim to reach the desired depth during the course of each tide. Your 1:1 ratio would take 25 tides based on 2m tidal range - this would result in a much cheaper solution but the average energy available throughout the year would be too low to be worthwhile. I do not think a 1:1,000 ratio would be well suited even in the unlikely event that it was feasible. The main reason being that costs would be prohibitive due to the increased Pontoon and Pulleys without a real benefit. The tidal range drops rapidly with increased ocean depth. The 25:1 ratio was not a random selection, it is based on achieving an optimum RoI with the conditions found off the coast of the UK.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 25/11/2011 21:38:25

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.
 

In terms of thermodynamics the gear ratio is everything to do with the energy density of the working fluid in the turbine. It's the gear ratio that determines the energy density of the working fluid in the turbine by multiplying the tidal head by the gear ratio to produce the turbine head.

If you are only interested in the relationship between the turbine and the working fluid in the turbine you are confusing fluid dynamics with thermodynamics.

Interesting, then perhaps you would care to provide a reference to support your assertion?
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/11/2011 22:07:03

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.
 

In terms of thermodynamics the gear ratio is everything to do with the energy density of the working fluid in the turbine. It's the gear ratio that determines the energy density of the working fluid in the turbine by multiplying the tidal head by the gear ratio to produce the turbine head.

If you are only interested in the relationship between the turbine and the working fluid in the turbine you are confusing fluid dynamics with thermodynamics.

Interesting, then perhaps you would care to provide a reference to support your assertion?

Why don't you simply explain why the gearing ratio and the energy density of the turbine working fluid are irrelevant in terms of thermodynamics? Should we assume that you have invented a system that is is exempt from the laws of thermodynamics? That's what your statement implies.

Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 25/11/2011 22:22:56
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 26/11/2011 08:47:28
Your 1:1 ratio would take 25 tides based on 2m tidal range - this would result in a much cheaper solution but the average energy available throughout the year would be too low to be worthwhile.

No, assuming there is no difference in efficiency, it wouldn't make the slightest difference to the total energy output during the year, or to average power output during the year.

What it would do is reduce mechanical inefficiency in the pulley system at the expense of a much larger turbine and storage vessel. As the storage vessel would have to be as large as the displacement of the pontoon, it would probably cost a bit more than the pontoon, so it would hardly be "a much cheaper solution".
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/11/2011 11:05:42

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.
 

In terms of thermodynamics the gear ratio is everything to do with the energy density of the working fluid in the turbine. It's the gear ratio that determines the energy density of the working fluid in the turbine by multiplying the tidal head by the gear ratio to produce the turbine head.

If you are only interested in the relationship between the turbine and the working fluid in the turbine you are confusing fluid dynamics with thermodynamics.

Interesting, then perhaps you would care to provide a reference to support your assertion?

Why don't you simply explain why the gearing ratio and the energy density of the turbine working fluid are irrelevant in terms of thermodynamics? Should we assume that you have invented a system that is is exempt from the laws of thermodynamics? That's what your statement implies.

I didn't think you would be able to provide a reference for your assertion but rather than concede the point you choose to paraphrase? Unless we can agree on the meaning of the thermodynamic terms the discussion will continue to be an argument in semantics i.e., utterly pointless.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/11/2011 11:09:25
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/11/2011 11:15:40
Your 1:1 ratio would take 25 tides based on 2m tidal range - this would result in a much cheaper solution but the average energy available throughout the year would be too low to be worthwhile.

No, assuming there is no difference in efficiency, it wouldn't make the slightest difference to the total energy output during the year, or to average power output during the year.

What it would do is reduce mechanical inefficiency in the pulley system at the expense of a much larger turbine and storage vessel. As the storage vessel would have to be as large as the displacement of the pontoon, it would probably cost a bit more than the pontoon, so it would hardly be "a much cheaper solution".

Typically, there are (2) tides per day.

The ocean depth is a function of the tidal range. 

The gearing ratio has to be matched to achieve the desired depth in one tide if optimum average energy output is to be achieved. Gear it too low and several tides are required before a generation phase can be run, i.e., the machine is under utilised. Gear it too high and the cost of the Pontoon and speed of descent is overrated.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 26/11/2011 16:07:40
Mootle,
You cannot change the tidal range (for any given location) and so, for any give size of pontoon the energy available per tide is fixed.
The gearing cannot change the energy.
Averaging that energy, for example over the course of the year to allow for neap and spring tides, doesn't change it.
The gearing doesn't enter into it.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 26/11/2011 21:27:25
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.

I'm sure they do, but the average energy of your system better be zero, or some very interesting things are going to happen.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/11/2011 21:59:41
Mootle,
You cannot change the tidal range (for any given location) and so, for any give size of pontoon the energy available per tide is fixed.
The gearing cannot change the energy.
Averaging that energy, for example over the course of the year to allow for neap and spring tides, doesn't change it.
The gearing doesn't enter into it.

I'm not saying the input average energy is changed, I'm only interested in the output average energy. You clearly understand the theory so perhaps I've taken your ability to apply this to this application for granted.

If the ratio is not properly matched to the prevailing tidal range, desired depth, generating duration etc., much of the available energy will not converted. The aim is to complete each system cycle (descent, generation, ascent, purge,) with each tidal cycle in order to optimise the convertion of energy. If the ratio is too small several tidal cycles will be necessary to complete one system cycle this will greatly reduce the average energy.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 26/11/2011 22:00:38
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.

I'm sure they do, but the average energy of your system better be zero, or some very interesting things are going to happen.

Why?
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 27/11/2011 10:11:28
The average energy is zero because it stores energy from the tide but gives it up to the generator.
The input and output have to balance so the net stored energy is zero.
However this talk of "average energy" is meaningless, for a start, average with respect to what?

There's still absolutely nothing that gearing can do to affect the energy provided by the tide.
All it can do is waste a bigger or smaller part of that energy..
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 27/11/2011 16:17:53
The average energy is zero because it stores energy from the tide but gives it up to the generator.
The input and output have to balance so the net stored energy is zero.
However this talk of "average energy" is meaningless, for a start, average with respect to what?

There's still absolutely nothing that gearing can do to affect the energy provided by the tide.
All it can do is waste a bigger or smaller part of that energy..

Geezer managed that without moving his fingers.

You're describing energy balance and I think we've already covered this and are in violent agreement.

I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output.

The success or failure of the system would in practical terms depend on the average energy output since it is this which determines the available revenue. It is in this respect that the selection of the gearing ratio has a huge impact.

We can continue with circular arguments of semantics or we can move forward by discussing something which actually matters. If the answer is let's argue about nothing some more then I think it would be better to draw the thread to a close.

If there are any new questions about the schematic animation or concept design then I'm all eyes.

If you have questions about the detailed design I would be happy to speculate but if it's hard facts you're looking for I'm afraid that would have to wait until the design has been developed.
Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 27/11/2011 16:58:26
"I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output. "

Do you really not see the contradiction there?
The energy input is the same as the energy output. Averaging doesn't make any difference (or, indeed, very much sense).
(or have you really given up on thermodynamics?)
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 27/11/2011 17:39:40
"I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output. "

Do you really not see the contradiction there?
The energy input is the same as the energy output. Averaging doesn't make any difference (or, indeed, very much sense).
(or have you really given up on thermodynamics?)

So your answer is to continue to argue about nothing of worth...

I don't think the continuation of this thread to be a worthwhile use of 'our' time at this stage.

Thank you to everyone for their valued input.

Signing off,

Mootle
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/11/2011 18:37:12
Mootle,

This is not a debate about semantics. If you consult those reputable books about thermodynamics you will appreciate that you have to define the complete system! Your system includes the pontoons, the gearing system, the storage vessel and the turbine.

The gearing absolutely will affect the power output because it affects the energy that can be recovered by the storage vessel.

You better have a equation somewhere that accounts for all the energy flowing in and out of your system (and it better average to zero in some timeframe) so that you can evaluate the effect of any changes you make. Any change affects the entire system, and you must account for the impact any change has on other parts of the system.

If you change the gearing, you absolutely will change its efficiency, and that means you will have more or less energy available to do useful work on the generator. If you lose more energy in the gearing system, you can still get the same amount of energy out of the generator, but you will have to make the pontoon even bigger to compensate for that loss. Considering how expensive the pontoon is going to be, that might not be a very good idea.

You continually take a microscopic view of one part of your system rather than a top down view of the entire system. If you don't do a total energy balance for the system as a whole you cannot possibly determine what the optimum gear ratio is.
Title: Will this buoyancy engine-based generator work?
Post by: Mootle on 27/11/2011 19:25:39
Mootle,

This is not a debate about semantics. If you consult those reputable books about thermodynamics you will appreciate that you have to define the complete system! Your system includes the pontoons, the gearing system, the storage vessel and the turbine.

You should appreciate from my prior replies that I fully intend to define the complete system. Apologies for any frustration caused by a unwillingness to prematurely enter into detailed design elements but if you're of the mind to continue this later I will return once the scaled animation is complete.

The gearing absolutely will affect the power output because it affects the energy that can be recovered by the storage vessel.


I would concede that there are any number of tunes we could play but this is not the way I would look at it. The gearing will affect the average energy output but the only impact on power output is the availability. It is the working head and flow rate that governs the power output for this system so for the 2m tidal range and 50m desired depth if we choose a 1:12.5 ratio it would take two tidal cycles rather than one (@25:1) for the Storage Vessel to reach the desired depth, i.e., the average energy output would be halved or in other words the same power output would be available for half the time.

You better have a equation somewhere that accounts for all the energy flowing in and out of your system (and it better average to zero in some timeframe) so that you can evaluate the effect of any changes you make. Any change affects the entire system, and you must account for the impact any change has on other parts of the system.

During the course of the first few pages of this thread we have looked at three check calculations which all served to demonstrate that the energy balance is theoretically sound. As the design develops I will aim to calculate realistic efficiency losses for each element of the system and if you are of a mind to check over my work that would be much appreciated.

If you change the gearing, you absolutely will change its efficiency, and that means you will have more or less energy available to do useful work on the generator. If you lose more energy in the gearing system, you can still get the same amount of energy out of the generator, but you will have to make the pontoon even bigger to compensate for that loss. Considering how expensive the pontoon is going to be, that might not be a very good idea.

It is true that it gets harder to maintain efficiency as the gearing ratio increases but the efficiency of the pulley system will depend (within certain bounds,) on the engineering. It is essential that the best fit is found in terms of revenue, cost and efficiency for the given arrangement.

You continually take a microscopic view of one part of your system rather than a top down view of the entire system. If you don't do a total energy balance for the system as a whole you cannot possibly determine what the optimum gear ratio is.

Thanks for the summary. I thought we'd covered this (somewhat fractiously,) within the first few pages of the thread but in anycase I would once again thank you for your input. As with BC above we're covering old ground so propose to bid you adieu for now.

Signing out,

Mootle



Title: Will this buoyancy engine-based generator work?
Post by: Bored chemist on 27/11/2011 20:02:15
It may be some sort of progress that he's talking about gears, but I think it was mentioned some time ago.
It seems much simpler to hang a big heavy float in the sea and let it rise and fall with the tide. Tie a rope to it and then connect that rope to a pulley. Have the other end of the pulley connected to a spring (or a counterweight).
When the tide falls it pulls the rope and turns the pulley. When the tide falls the spring or counterweight pulls the rope and turns the pulley the other way.
With this system there is less rope, it's all above water (and so is everything else apart from some sort of frame to hold it in place.)
Your system looks unduly complicated. Why have 6 ropes + pulleys when you can just put a gearbox on the generator shaft?

I wonder if I will ever get an answer to that question.
Title: Will this buoyancy engine-based generator work?
Post by: Geezer on 27/11/2011 22:51:39
Quote
The gearing will affect the average energy output but the only impact on power output is the availability.

Average energy means there are changes in energy in time. In other words, between time x and time y there was a change of z joules. A change in energy in a certain amount of time is a measurement of power. It might be joules per second (watts), joules per hour, BTUs per month, or calories per tide, but it's still a measure of power.

Therefore we can rewrite your statement as;

"The gearing will affect the average energy power output, but the only impact on power output is the availability."