[Geezer]

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?

[Geezer]

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

[Bored chemist]

"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.

[Mootle (OP)]

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%.

[Mootle (OP)]

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.

[Mootle (OP)]

"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.

[Geezer]

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?

[Geezer]

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?

[Mootle (OP)]

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.

[Geezer]

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  []. 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.)

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?

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?

[Bored chemist]

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.

[damocles]

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!

[Bored chemist]

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.

[Mootle (OP)]

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  []. 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.)

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?

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.

[Mootle (OP)]

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.

[Bored chemist]

"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.

[Geezer]

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.

[Mootle (OP)]

"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.

[Mootle (OP)]

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?

[Geezer]

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.