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Penelope Anderson

Tidal power

I was born on the west coast of Scotland, where the tides rip up and down the coast and between the islands all day and every day. They power what is at present the largest whirlpool in the northern hemisphere, the Corrievrechan. This kind of power should be used.
I have never seen much serious discussion about harnessing the energy of these immense tides, which are more constistent and steadier than waves because waves depend a lot on wind power. Are there any ideas about using this energy, and what are Downsizer opinions?
Behemoth

There have been reasonably serious proposals to use tidal power in the Severn Estuary but it's been hampered by environmental concerns. Don't know much beyond that. It's 25 to lunch, no point in doing some work, I'll have a ferret on the Defra website.
Jonnyboy

Behemoth wrote:
There have been reasonably serious proposals to use tidal power in the Severn Estuary but it's been hampered by environmental concerns. Don't know much beyond that. It's 25 to lunch, no point in doing some work, I'll have a ferret on the Defra website.


I have admit to being biased here, the proposed tidal system on the Severn would stop the tidal bore, a wonderful phenomenon, which I happen to enjoy surfing for a few miles at a time.
Penelope Anderson

Jonnyboy, do you know what the design for the Severn bore looks like? I'm sure they could come up with something that would allow it to run freely if they used their thinking caps.
Behemoth

Quick look doesn't throw up anything that's not buried in a dense report.
Jonnyboy

Penelope Anderson wrote:
Jonnyboy, do you know what the design for the Severn bore looks like? I'm sure they could come up with something that would allow it to run freely if they used their thinking caps.


Any barrier would have to be 'not there' on the incoming tide and have allowed all the water out on the outgoing tide before it turns. It just isn't feasible without preventing the bore.

The bore works as the volume of water is too great for the suddenly narrowing and shallowing river channel above sharpness, thus it rushes upstream as the bore.

At times when I surfed it, it has been 5-6ft high and I've had one ride that lasted for over 3 miles. It's an awesome spectacle.
dougal

Re: Tidal power

Penelope Anderson wrote:
...on the west coast of Scotland, ... the tides rip up and down the coast and between the islands all day and every day. ... This kind of power should be used.
I have never seen much serious discussion about harnessing the energy of these immense tides, ...

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.

As regards the use of *strong* tidal currents, part of the problem is the scale of the civil engineering needed to withstand those selfsame forces!
It seems more economically productive to harness milder, rather than wilder, forces.

There's a review of some current thinking (sorry 'bout that!) on wave and tide power here:
http://www.fujitaresearch.com/reports/tidalpower.html
Penelope Anderson

Had a quick look at the Fujita web-site and found most of the designs too bulky. As you say, they would stop things like the Severn bore in its tracks. Even the underwater tidal farm is not completely underwater. If they could solve the problem and design a less rigid structure, which is completely submerged. one which does not resist the water (like the electricity carrying wires on the dread pylonswhich sway in the wind) and which has those "spinners" attached to it which would generate the power. Some research would have to be done on the effect on fish - they are always rather inquisitive!
Behemoth

Re: Tidal power

dougal wrote:
It seems more economically productive to harness milder, rather than wilder, forces.


Wasn't this the problem with some early wave power stations, in that they went for places with big waves and got smashed.
dougal

Penelope Anderson wrote:
.. If they could .. design a less rigid structure, which is completely submerged. one which does not resist the water ...

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

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

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.
http://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

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

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

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

A story tonight from the BBC
http://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

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 Laughing
Nick

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? Smile

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

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

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

Ah, what the hell - patent it anyway Laughing
tahir

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? Smile


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

I abdicate all reponsibility.

Shane - the problem is that you can't produce *power* from hydro*static* pressure. Just hydro*dynamic* 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

That's why I said the change in hydrostatic head as the tide goes in and out Wink
tahir

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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