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On Wed, 30 Sep 2009 09:32:47 +0100, The Natural Philosopher wrote:

Proposed Bristol channel tidal barrier 7GW

For how many hours a day?

Some power close to 24/7, reaching maximum power for at least
half that time.

But probably not when it's needed, OK ship it up to Scotlands pumped
storage schemes then ship it back down? Wonder how much wouldbe lost?

Or alternatively to cause less of an environmental impact, and
better
access for shipping, a row of tidal underwater turbine towers
across
the Bristol channel, producing around half that power

At what cost?..both direct, and indirect to the coastline and
environment.

A barrage is probably nota good idea, the severn estuary is very
silty, slow the flow of water (which with 40' tides is huge, hence
being a good site for power generation) and the silt will start to
settle out. Dredging such a huge area is not very practical.

Tidal lagoons or submerged turbines in a weir type arrangement is
probably better from the long term maintenace and enviroment aspects.

--
Cheers
Dave.

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charles wrote:
In article , Steve Terry
wrote:

"[email protected]" wrote in message
...
"Steve Terry" wrote in message
...

Proposed Bristol channel tidal barrier 7GW
For how many hours a day?


Some power close to 24/7, reaching maximum power for at least half that
time.

and it would provide a new motorway (and or railway) between England and
Wales along the top of it

Or alternatively to cause less of an environmental impact, and better
access for shipping, a row of tidal underwater turbine towers across the
Bristol channel, producing around half that power

another tidal barrier across the Mersey could produce 1.5GW

The French built a tidal generator in Brittany many years ago. Why did
they never build any more? Did it not work as planned? Did sea water rot
the turbines? Was it simply too expensive compared with nuclear? Does
anyone know?

I suspect its as with all these renewables, a mixture of things.

1/. Low energy density. Its very hard to extract energy from a source of
lot of something slightly different rather than a little of something
highly different, in energy from your sink . Wind, solar and tidal and
indeed broadly hydro, all represent essentially solar incidence over
very wide areas representing loads of energy, but spread very thin. Only
occasionally do geographical quirks collect it for use in a convenient
place.

That inevitably means BIG installations costing a lot for not that much
power. CF a typical roof top windmill that produces a few watts,
compared with say a small petrol engine you can buy for less than £100
capable of a few KW..



2/. By their very nature, tidal power stations have to be designed
specifically for the actual place they reside..the tide flows and so on
are radically different in different locations, its also new technology,
and that means no low cost mass produced components and a legacy of R&D
in the form of stock solutions, exist.

So once again that is doomed to make them costly.

3/. Risk benefit analysis., If you do not simply subsidise, its a brave
man who reaches into his pocket for a project with very poorly defined
risk, even if the rewards look good on paper. (Channel Tunnel vision)
That's what's holding back nuclear power right now. There is an element
of political risk, power stations can be (and have been) closed, at a
political whim.


4/. Political subsidisation, which seems a good idea, is in reality a
further risk. This was brought home to me, clearly, when I attended an
alternative energy conference some years back. At lunch I got talking to
a German banker. His question to me was 'You are an engineer, tell me,
is any of this viable without subsidy?' and I had to tell him that no,
it was not. 'Ach, then I am wasting my time, my banks time and my
investors money' he said. 'The politicians will never let us make a
profit: If we do, Boom! there is a row and the subsidies are cut'.

A situation you can see clearly with BT today. Ofcom wont let them make
serious money, and complains that they wont undertake serious investment.

Also to be seen with the Dartford crossing on the M25. Once it had paid
back its investors principle, and they looked set to make a profit, it
was to be effectively nationalised..strangely, that happened, but under
Nu Laber, tolls are still being charged. Hmm.


Put that in the pot and stir it, and you have a situation that nearly
all alternative energy is a commercial risk not worth taking by and large.

Not for private investors OR for governments.


Even conventional energy is subject to some pretty twisted economics.
I am not an oil market specialist, but it seems that the laws of supply
and demand don't work in the oil industry. If the price is high, you
would expect people to pump more oil, drill more wells and supply more
oil. It seems to be almost the reverse. By pouring billions into
developing less and less productive wells (mots oil still comes from the
huge easy fields exploited years ago) you are in fact ending up spending
money to both depress the price of oil, and deplete your capital assets
- your reserves.

So there you have it. Governments wont, and indeed these days can't
finace massive infrastructure out of the public purse, but because its
deemed of 'national importance' neither will they refrain from
interfering with it if someone else does it.

The net result is that nothing happens.


The ONLY reason windpower has become fashionable is because the EU
simply made vast sums of money available to meet a self imposed
political emissions target. A vast sum we are all having to pay in
increased taxes.

typical political interference. ALL they had to do was tax fossil fuels
by about +50% more and let the market decide how and where it would make
the cost savings..

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The Natural Philosopher wrote:
Wind, solar and tidal and
indeed broadly hydro, all represent essentially solar incidence over
very wide areas representing loads of energy, but spread very thin. Only
occasionally do geographical quirks collect it for use in a convenient
place.

If you are claiming (it's a bit unclear) that tidal energy is a derived
form of solar, i.e. derived from the light emitted by the sun, and
incident on the earth, you are mistaken.

Wind and hydro _are_ solar, though.


#Paul

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The Natural Philosopher wrote:
If you are claiming (it's a bit unclear) that tidal energy is a derived
form of solar, i.e. derived from the light emitted by the sun, and
incident on the earth, you are mistaken.

No. I admit to a gross over simplification there.

Tidal energy is derived from gravitational potential energy and/or
the kinetic energy of the earth/moon/sun system. I think describing your
remark as an "over simplification" is being a bit optimistic.


#Paul

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In article ,
wrote:

If you are claiming (it's a bit unclear) that tidal energy is a derived
form of solar, i.e. derived from the light emitted by the sun, and
incident on the earth, you are mistaken.

A substantial part of the tides are caused by the sun's gravity.
Without the moon, we would still have tides - about a quarter of
the height, I believe.

-- Richard
--
Please remember to mention me / in tapes you leave behind.

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On Sep 30, 12:58*pm, Paul Martin wrote:
In article ,
* * * * Richard Tobin wrote:

In article ,
wrote:
If you are claiming (it's a bit unclear) that tidal energy is a derived
form of solar, i.e. derived from the light emitted by the sun, and
incident on the earth, you are mistaken. *
A substantial part of the tides are caused by the sun's gravity.
Without the moon, we would still have tides - about a quarter of
the height, I believe.

Other way round. The moon has the largest effect,

That's why taking away the moon leaves only a quarter!

MBQ

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Paul Martin wrote:
In article ,
Richard Tobin wrote:
In article ,
wrote:

If you are claiming (it's a bit unclear) that tidal energy is a derived
form of solar, i.e. derived from the light emitted by the sun, and
incident on the earth, you are mistaken.

A substantial part of the tides are caused by the sun's gravity.
Without the moon, we would still have tides - about a quarter of
the height, I believe.

Other way round. The moon has the largest effect, and the sun the
lesser effect.

that's what he said. About a quarter with no moon, ergo 3/4 is the moon.

Of course if we start using the tidal energy, the moon will come
crashing into us and destroy the planet a bit quicker. Another example
of 'green' energy destroying the planet...? ;-)

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On Wed, 30 Sep 2009 15:11:20 +0100, The Natural Philosopher wrote:

Of course if we start using the tidal energy, the moon will come
crashing into us and destroy the planet a bit quicker. Another example
of 'green' energy destroying the planet...? ;-)

He he, except that the moon is currently moving away from us at about
3.8cm/year. As you take energy out of the system there is less to
alter the course of the moon so it tends to travel a straighter path
and thus moves away, well it's a theory...

--
Cheers
Dave.

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On Wed, 30 Sep 2009 12:58:54 +0100, Paul Martin wrote:

A substantial part of the tides are caused by the sun's gravity.
Without the moon, we would still have tides - about a quarter of
the height, I believe.

Other way round. The moon has the largest effect, and the sun the
lesser effect.

I believe that's what he said... 1/4 sun, 3/4 moon.