Tidal power

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Tidal power
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Penelope Anderson

Joined: 21 Sep 2005
Posts: 326
Location: london

Posted: Sat Jan 07, 06 10:39 am Post subject:

Yes, thanks, dougal, I think I've got that principle into my fat head! But I still think that the SUPPORTING structure should be less rigid, NOT the actual generators. It's awfully difficult to explain what I mean without drawings.I just have a bee in my bonnet about tidal power I suppose. So many good intentions in that direction have become bogged down by apathy and questions of economic viabilty. They have a wave power machine in St Malo - the French always seem to be miles ahead, the solar power generating panels in the Pyrenees for example have been there for 50 years or so.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Sat Jan 07, 06 11:55 am Post subject:

Penelope Anderson wrote:

... I still think that the SUPPORTING structure should be less rigid, NOT the actual generators.

The support has to 'support' the drag from the generators, and therefore needs to be immensely *strong*.

Large scale engineering doesn't do strong together with flexible very well.

Turbines on flexible supports will suffer from more turbulent flow than their more rigidly mounted competition. A turbulent flow will give even more drag for less power usefully generated. Turbulence will also produce varying loads on bearings, blades, etc - indeed the whole construction would be subject to fatigue loadings. Remember that, generally, civil engineering structures are designed to be always in compression - because economic construction materials simply don't "do" tension...

Penelope Anderson wrote:

... the French always seem to be miles ahead, the solar power generating panels in the Pyrenees for example have been there for 50 years or so.

Umm? Power generating for 50 years?
For about that time period, there has been a *high_temperature* *research* facility at Mont-Louis then Font-Romeu in the Pyrenees, with the world's largest solar furnace - having a hillside covered with steerable mirrors. It's a giant version of using a magnifying glass to light a fire... It can produce a heating effect of 1000kW, but its NOT electricity generation from solar power.
https://www.imp.cnrs.fr/solface/index.php?page=rubrique_3
Is that what you were thinking of?

As a result of decisions taken in 1974, France in fact currently obtains 75% of its electricity from nuclear power.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Sat Jan 07, 06 12:05 pm Post subject:

dougal wrote:

There has been a tidal power station in operation for about 40 years at La Rance, near St Malo in Brittany (France).
The objections to such schemes have been largely environmental.
My personal opinion is that some localised environmental change is preferable to global change.

Penelope Anderson wrote:

They have a wave power machine in St Malo - the French always seem to be miles ahead...

Could you provide a reference to the *wave* power station? I'm only aware of the *tidal* generation station that I had referred to earlier.

Penelope Anderson

Joined: 21 Sep 2005
Posts: 326
Location: london

Posted: Sat Jan 07, 06 2:55 pm Post subject:

Oh dear, I seem to be getting my terminology mixed up - I did mean tidal not wave, power. Sorry Dougal.
When I visited the Pyrenean site 46 years ago, and actually saw those giant mirrors I was told they were going to be generating electricity in the near future. Either its not the near future yet or my companions were misinformed.
Have taken on board what you say about structural resistance - I suppose all this will have to wait until someone comes up with an environmentally friendly design to which no-one on earth can object.

gingerwelly

Joined: 08 Dec 2005
Posts: 419
Location: Wales ...in cardiff at the mo but from mid wales

Posted: Sat Jan 07, 06 7:55 pm Post subject:
with the severn estury proposal, one of the main probs was the high sedimentation rates,the build-up of sediment would be too rapid, and stop the turbines turning. But with the 2nd highest tidal range in the world it has the potential to provide a solution for the UKs future energy problems. But as with most things there will be a cost, the loss of habitat and the severn bore been one of them.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Wed Jan 25, 06 12:21 am Post subject:
A story tonight from the BBC https://news.bbc.co.uk/1/hi/sci/tech/4645452.stm The Carbon Trust believe that 20% of the UK's energy could come (economically) from tidal+wave power. There's a prototype of a novel tidal powered generator to be installed this year in Northern Ireland. See the links from the BBC page...

Shane

Joined: 31 Oct 2005
Posts: 3467
Location: Doha. Is hot.

Posted: Wed Jan 25, 06 8:35 am Post subject:

I guess it doesn't work, cos it would have been tried, but I would have thought you could generate power from the change in hydrostatic head as the sea level changes during a tide. If so, you could have your power plant completely submerged, as the generating equipment would have to be on the seabed to work. "All" you'd have to do is convert the hydrostatic head into pressure and use the changing pressure to drive your generator. Or maybe wait for the new materials that are being developed that generate a small current when they are deformed and use those.

Nothing like a good ponder first thing in the morning

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Jan 25, 06 9:18 am Post subject:

dougal wrote:

It is only by resisting the flow that power can be generated.

Dougal, is this basic physics, or a call to revolution and civil unrest?

I've often thought that as we live on a bunch of islands and a huge mass of water rocks up and down twice a day, there must be some way of harnessing this energy which is free, sustainable and clean.

The cost is likely to be upsetting a few fish (doubleplus glib), but would it be worse than belching smoke and CO2 out?

Another idea struck me the other day, about wind power. Would it be possible to put some kind of wind turbine on cars. Think a tunnel, or similar along the length of a car, containing blades to generate extra energy for the car, even just for the electrics, rather than the engine, perhaps to run the AC. Is it a really dim idea? I guess it would depend on the efficiency of wind v petrol energy production, and working out any fuel economy loss due to extra drag. And would it be terribly noisy inside the car?

If anyone does the figures, and sells it to Honda, I want a cut.

Shane

Joined: 31 Oct 2005
Posts: 3467
Location: Doha. Is hot.

Posted: Wed Jan 25, 06 10:12 am Post subject:

You'd be using the power from the car engine to generate the additional thrust required to pull the turbine through the air, surely? So you'd be converting chemical energy (petrol) into kinetic energy (engine - 30% efficiency?) and then be suffering a further loss to move the car forwards (~15% power loss from crank to axle?). The increased drag would mean that you'd need additional power (i.e. more petrol) to maintain the same speed (I think a roof rack adds ~5% to fuel consumption, so might be around that level). Then you'd use the forward motion of the car through the air to drive a turbine to convert kinetic energy into electricity, which you'd then covert into chemical energy (battery) and back into kinetic energy. Can't see it being anywhere near as efficient as the current hybrid engines, which use the forward motion of the car when the engine is unloaded to charge batteries.

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Jan 25, 06 10:17 am Post subject:
Yeah, that's the plan. As I said, I've no idea about the relative efficiencies, but there's no harm in asking the question. So, what you're saying is that I'll need another scheme to get really, really rich, and this isn't the one? Bugger.

Shane

Joined: 31 Oct 2005
Posts: 3467
Location: Doha. Is hot.

Posted: Wed Jan 25, 06 10:21 am Post subject:
Ah, what the hell - patent it anyway

tahir

Joined: 28 Oct 2004
Posts: 45676
Location: Essex

Posted: Wed Jan 25, 06 10:52 am Post subject:

nickhowe wrote:

dougal wrote:

It is only by resisting the flow that power can be generated.

Dougal, is this basic physics, or a call to revolution and civil unrest?

Dunno but if its the latter we need a leader, I vote for Dougal

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Wed Jan 25, 06 11:37 am Post subject:
I abdicate all reponsibility. Shane - the problem is that you can't produce power from hydrostatic pressure. Just hydrodynamic flow. Nickhowe - car windmills - no. Just no! As shane said, the most efficient conversion of fuel chemical energy into kinetic energy (speed) and potential energy (going up hill) is going to be the most direct conversion.

Shane

Joined: 31 Oct 2005
Posts: 3467
Location: Doha. Is hot.

Posted: Wed Jan 25, 06 1:10 pm Post subject:
That's why I said the change in hydrostatic head as the tide goes in and out

tahir

Joined: 28 Oct 2004
Posts: 45676
Location: Essex

Posted: Sun Feb 05, 06 1:41 pm Post subject:
Radio 4 Friday 15:00 Changing Places Wave Power: With the ongoing development of alternative sources of renewable energy, Dylan Winter explores the power of the tide and plans for barrages on British estuaries and rivers.

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