Generating Power

[naomi24]

With all the controversy over fracking, nuclear power, etc, etc., with a good deal of the earth covered in water, it seems to me that with a little innovation, we have potentially all the power we'll ever need. Why can't we harness the power of the sea?

[KARL]

.........and all this use of solar energy (including wind) is snuffing out the sun.....

[jim360]

I suppose technically it is -- after all, the reason the Sun is due to burn out in 5 billion years or so is because it's burning through its energy, and that energy is being dumped into space, and if we suck that energy up faster and more efficiently in our patch... I may try and check this some time, not sure it's really the same thing.

More seriously, though: the Moon is receding from Earth gradually, due to energy loss from e.g. tides, and if we did extract yet more energy from the tides then the Moon would recede faster, but off the top of my head I doubt it would make any significant difference unless we were using tidal power whenever and wherever it was possible to do so, across the whole world. Even then I don't think the energy thus extracted would be (any more than) comparable to that already lost due to friction with the seabed.

Tidal power is, or ought to be, part of the answer to our energy needs, but not all of the answer. The potential environmental damage is one reason, though we've done enough to devastate large parts of the ocean and the Earth already. Also, it's not a good idea in practice to rely solely on a single form of energy, especially one such as tidal, because of the risk of something going wrong (either by accident or as a deliberate attack) -- with only that as a source of energy, such an accident could be a major disaster. Let alone the cost to set the thing up in the first place, or to maintain it. Meanwhile most renewable sources of energy find it difficult to cope with changes and surges in demand such as the "half-time in a football match" or "just before the next episode of Corrie" surge, when everyone watching goes and puts the kettle on. For such surges you need either to develop a way of efficiently storing energy that can also be called upon quickly, or an energy source that can be controlled as needed. At the moment only certain HEP stations and conventional fossil fuel power stations (and, to some extent, nuclear power stations, see below) can cope with these rapid surges, but the technology is expanding into diverse renewable sources also.

The key word, though, is diverse. Relying on just a single source of energy, however attractive, is not the answer.

A few sources:

http://www.darvill.clara.net/altenerg/pumped.htm

http://www.nationalgrid.com/NR/rdonlyres/49736B61-06E4-4241-AF0B-8E7D84053AF7/1227/Nick_Easton_A_day_In_The_Life_Of_.pdf

http://www.claverton-energy.com/nuclear-power-is-flexible-in-its-output.html

http://www.kombikraftwerk.de/index.php?id=27

[bert_h]

For jim360 and others - efficient storage and re-release of generated energy is the outstanding problem in all of this. Tidal energy goes from its peak to zero twice a day. Nuclear fission power stations work best at a steady load. Nuclear fusion as intended at ITER will work in successive huge bursts of an hour or two at a time. Wind, wave and solar power all generate at irregular rates. The pumped storage facilities at Ben Cruachan, Dinorwic, and a couple of other sites are the perfect way to match the domestic demand cycle to these non-matching rates of generation, but we would need about twenty times as much of it as we've got. There are research projects being planned to find more ways of rapidly storing and releasing energy. It baffles me why the green energy enthusiasts don't realise that this is such an important part of making their dreams workable in practice.

[Khandro]

Something I can't understand - I'm sure someone can enlighten me; In a nearby village to me is an 'old fashioned' water wheel about 10 meters in diameter, it is not a direct drive to the machinery, rather it is attached to a large generator/dynamo from which the saw is driven electrically. When the saw isn't in use, the electricity is somehow re-directed to the small village and is sufficient to make a significant contribution "enough to keep several house supplied".
Question; Energy has been abstracted from what is quite a small stream, but the stream flows on seemingly at the same speed as before, So could a second, or indeed several similar wheels be placed in sequence?

[naomi24]

I was thinking more of, say, offshore platforms that would work fundamentally on the principle of simple watermills. As Jake says, the problem is in storing the electricity, but politics and initial costs aside, if that could be cracked there is an endless supply to be had there - and I don't see how that would have any effect on the moon.

[jim360]

Seems that you have something like this in mind then:

http://en.wikipedia.org/wiki/Tidal_stream_generator

Not sure what the current status of a lot of the projects referenced is, though. As to how it might affect the moon:

http://en.wikipedia.org/wiki/Tidal_acceleration

Putting more and more turbines into the water would almost certainly add to this effect, but as I have said earlier (although without the figures to back it up) I doubt that our own impact would be all that significant. The dissipation due to friction with the seabed is of order terawatts (10^12 Watts), and even assuming a maximally efficient use of the available tidal energy I don't think we reach this level, but something closer to order 10 gigawatts, which is roughly 100 times smaller. So if we made the use of all available tidal power you might be able to measure a difference in the Moon's motion, but not much of one.

* * * * * *

Actually a more serious issue with this post about tidal power is that it doesn't appear to provide "all the power we'll ever need". Assuming I have interpreted these figures correctly, then the total global energy demands in 2008 are of order 500 times larger than the (estimated) available energy from the ocean (which, in itself, is mainly from using the ocean's heat, rather than tidal power).

NB: These figures are based on a wikipedia article, but on investigating the source I'm not convinced that those figures are correct. I'll update in due course if I find out what's gone wrong, but what I think are the right figures still give a significant shortfall between potential tidal energy and annual energy consumption (but closer to 5 times smaller rather than 500!)

[EDDIE51]

bert_h, I agree with your post about the Moon being drawn further away from Earth but surely the effect is minuscule, around 1cm in 1,000 years ? The Moon is already moving away from Earth at around 2 cm per year , this can be verified by using the laser reflectors left on the Moon by the Apollo spacecraft for that purpose. The effect due to any tidal power must be several orders of magnitude less?

[bert_h]

@EDDIE51 - you're quite right, it's minuscule, as confirmed by an earlier post in this thread; but it is not zero. I was just being a bit pedantic with someone else's assertion of "an endless supply", because the energy actually has to come from somewhere. I was explaining where from, and why the supply was - strictly speaking - limited.

[heathfield]

Roll on nuclear fission!

[jim360]

Fusion, surely? We already use nuclear fission.

[Khandro]

Please can anyone answer my question of 13:00. i.e. Why can we not have a succession of water-wheels along a river? Does the water need some distance after one wheel to recover it's potential power? it doesn't appear so.
Watching a log being sawn in length just by the power of a stream is truly awe-inspiring.

[heathfield]

You're right, Jim. 'Fusion' of course! Doh. Silly me!

[jim360]

I'll have to think about it a bit, Khandro. I mean, I'm sure there are some rivers around which do have several wheels along them, but there's going to be a sort of diminishing returns effect going on at some point, as each wheel extracts energy from the flow and there is only so much energy available. Probably, if the wheels are spaced out enough, this would not matter -- but how much "enough" is will depend on the specific river, and on the size of the wheels being used.

[Khandro]

jim; I have an idea of a river with maybe say 100 wheels on either bank all connected to dynamos, compared to wind turbines they are cheap, they are possibly made of aluminium and concrete and do not depend on the vagaries of the elements and are 100% clean. One problem is that the one I describe is overshot, which presumably requires a steep incline, but undershot wheels could account for the change in river surface height by a rise and fall mechanism. I think water wheel technology may have been swept aside after the industrial revolution in favour of fossil fuel, producing steam. Maybe there is a reason against it, but I've seen it work marvellously on a small scale, why not make it work on a larger one?

[plowter]

Surely generating power isn't the problem? We need them scientists to invent a ginormous battery that can store all this energy.

[jim360]

Some things just don't scale, but without further study I can't really comment much further than:

-- to drive such a bank of turbines would require a very fast, very large river, but such a combination is pretty rare: rivers are fast when they are small(er), and large when they are slower.

-- And rivers are also fast in hills, or valleys, where it would be difficult to build such a large bank of wheels (due to access, for example, or just the fact that land is likely to be steep on the banks).

At any rate I don't expect that enough rivers would be suitable for it to be anything more than a local solution, and even then you would likely come up against cries of environmental damage or that the huge set of wheels is an eyesore, etc.

[New Judge]

Yes and it will slow down the rate of the earth's rotation, making for longer nights and more energy needed for light bulbs ! A non-starter therefore :-)

[New Judge]

Tidal barrages, that is ^^^.

And I learnt that for my 'O' Level Physics, thus proving conclusively that education has been dumbed down.

[seadogg]

Khandro, the power of water depends on the "Head of Water" which is a function of the speed and quantity. The speed is determined by the drop from source to point of use. In practice a water wheel by a river needs a millrace which feeds the wheel and may be quite a length thereby limiting the number of wheels in a stretch of the river. The actual power of a water wheel is relatively low on horsepower compared with electrically powered machinery.
The tailrace to a water wheel, carrying the water back to the river is usually slower than the millrace which brought the water.

[neodarwinian]

The University of Colorado is working on splitting hydrogen fro oxygen in water for the power released.

Still in the experimental stages but it looks promising.