[Geezer]

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  []

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 [])

[johan_M]

What do you mean by displacement efficiency? Where does the lost energy go?can you give a simple example?

[Geezer]

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.

[Mootle (OP)]

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.

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.

[Mootle (OP)]

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.

[Geezer]

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.

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.   

[Bored chemist]

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.

[Mootle (OP)]

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.

[Mootle (OP)]

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.

[Geezer]

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

[imatfaal]

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

[Geezer]

Is that similar to wedding tackle?

[Mootle (OP)]

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.

[Bored chemist]

"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.

[Geezer]

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.

[johan_M]

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.

[Bored chemist]

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.

[johan_M]

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.

[Geezer]

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.

[Mootle (OP)]

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.