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Author Topic: Will this buoyancy engine-based generator work?  (Read 75187 times)

Offline imatfaal

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Will this buoyancy engine-based generator work?
« Reply #150 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
 

Offline Geezer

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« Reply #151 on: 14/11/2011 19:12:29 »
Is that similar to wedding tackle?
 

Offline Mootle

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« Reply #152 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.
 

Offline Bored chemist

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« Reply #153 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.
 

Offline Geezer

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« Reply #154 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.
 

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Will this buoyancy engine-based generator work?
« Reply #155 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.
 

Offline Bored chemist

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« Reply #156 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.
 

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« Reply #157 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.
 

Offline Geezer

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« Reply #158 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.
« Last Edit: 16/11/2011 06:57:40 by Geezer »
 

Offline Mootle

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« Reply #159 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.
 

Offline Mootle

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« Reply #160 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
« Last Edit: 17/11/2011 18:21:17 by Mootle »
 

Offline Bored chemist

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« Reply #161 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.
 

Offline JP

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« Reply #162 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. 
 

Offline Geezer

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« Reply #163 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.
 

Offline Mootle

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« Reply #164 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.
 

Offline Bored chemist

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« Reply #165 on: 20/11/2011 18:38:08 »
OK, but the average power is determined by the size of the floats and the tidal range.
 

Offline Geezer

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« Reply #166 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).
 

Offline Mootle

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« Reply #167 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.
 

Offline Geezer

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« Reply #168 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.
 

Offline Mootle

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« Reply #169 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.
« Last Edit: 20/11/2011 21:08:32 by Mootle »
 

Offline damocles

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« Reply #170 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?
 

Offline Bored chemist

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« Reply #171 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.

 

Offline Geezer

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« Reply #172 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.)

 
 

Offline Bored chemist

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« Reply #173 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.
 

Offline Geezer

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« Reply #174 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.
 

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