
UK unveils plans for huge lagoon power plants stretching miles into the sea - AndrewDucker
http://www.independent.co.uk/news/uk/home-news/uk-unveils-huge-lagoon-power-plants-stretching-miles-into-the-sea-10079730.html
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pjc50
UK unveils _plans to build_ tidal power plants. We've been planning things in
the Severn Estuary my entire life and so far not lit a single lightbulb from
it. As all the comments on the BBC story say: get on with it, build the thing,
and tell us when it's done.

(There are a few tidal-power-through-undersea-turbines schemes in operation
off Scotland, I believe)

~~~
arethuza
There is a scheme just starting to be built in the Pentland Firth between
Caithness and Orkney:

[http://www.meygen.com/](http://www.meygen.com/)

I believe the first commercial tidal scheme of this type (effectively
underwater windmills rather than a barrage) was in Northern Ireland:

[http://www.marineturbines.com/3/news/article/7/seagen__the_w...](http://www.marineturbines.com/3/news/article/7/seagen__the_world_s_first_commercial_scale_tidal_energy_turbine_deployed_in_northern_ireland)

~~~
achamayou
There's been one in Brittany since the mid-sixties:
[http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station](http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station)

It works alright, but unless you have a very luckily shaped coastline, it
doesn't scale all that well. It's also subject to silting in the long run,
which isn't great for the yield, or the local eco-system.

~~~
arethuza
That's a barrage - like the scheme discussed in the original article. The NI
and Pendland Firth schemes don't rely on a barrage but on the very strong
tidal streams naturally found in those areas.

~~~
achamayou
Yes I know, I was responding to the OP mostly, since you'd already provided a
reference to underwater turbine schemes.

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jacquesm
That's _very_ little head. Does anybody have the engineering data on these
projects? Have they built a smaller installation to prove the concept?

Head height is a major factor in hydro power installations.

~~~
Brakenshire
There are some technical details about flow rates and head height in section
4.8 (p. 85/88) of this document:

[http://tidallagoon.opendebate.co.uk/files/TidalLagoon/DCO_Ap...](http://tidallagoon.opendebate.co.uk/files/TidalLagoon/DCO_Application/6.2_4.PDF)

One other thing I noticed upon briefly skimming is they're considering
installing turbines which can also be used as pumps. I suppose in principle,
at the cycle of the tide when the head is low and the plant isn't producing
power, you could use the same facility as pumped storage.

There's also a rather florid promotional video here, if anyone's interested:

[https://www.youtube.com/watch?v=mXEmHDQtXnw](https://www.youtube.com/watch?v=mXEmHDQtXnw)

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hanoz
What I don't understand about the idea is this. This stretch of water has one
of the highest tidal ranges in the world, but this presumably is a matter of
resonance, i.e the Bristol Channel and Severn Estuary just happen to be shaped
in such a way that their natural resonant frequency is a close match with the
driving force's twelve and a half hour odd period. But surely this means that
the extra energy in the water, over and above places with lesser tides, is not
something that can be tapped again and again each tide at any significant
scale, it's a one time only bonus in its potential and kinetic energy which is
gone after you extract its power through dampening. The ultimate non renewable
energy, gone in half a day!

Anyway, I'll be giving serious consideration to dragging my family out early
to see a five star Severn Bore the weekend after next, it could be the last
one ever.

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jbattle
That would be true if it were a freely oscillating system, but since the tide
is 'powered' by the moon I'd think the tidal cycle should keep going until the
moon stops orbiting. (though I'm not 100% sure I understand how tides work)

~~~
hanoz
I don't see that. Surely if you have two swings hanging from a swaying tree
and one of them is swinging wildly because it's the right length to resonate
with the moving branch above, you can't say hey this x kg tyre is rising and
falling y cm every s seconds, lets harness that. It only has the same
renewable energy as the other swing, plus a one time build up of energy that
its taken to get it up that extra height.

~~~
DanBC
But the moon is providing an input. So, for your swing example, there is
someone on one side giving it a push every pass.

~~~
hanoz
No one's pushing my swings! I've already accounted for the input, it's the
great mass of the swaying tree (and in turn the wind etc.), and like the
tides' moon it's the same input to both swings, only one's them is swinging
like the clappers whilst the other barely moves. Even though the former
clearly has more energy at a given point in time most of that is a one off
build up, and there can't be any more repeatedly extractable energy in the big
swinger than the small.

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dandare
FYI tidal power plants are slowing down Earth's rotation.
[http://physics.stackexchange.com/questions/6400/are-tidal-
po...](http://physics.stackexchange.com/questions/6400/are-tidal-power-plants-
slowing-down-earths-rotation)

~~~
bjelkeman-again
The movement of the oceans, and flexing in the earth crust, also slows down
earth's rotation. But we are talking milliseconds per century. [1] So, tidal
power plants are going to have a very small effect overall.

[http://en.wikipedia.org/wiki/Tidal_acceleration](http://en.wikipedia.org/wiki/Tidal_acceleration)

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PuffinBlue
This article reads like it was written by an 11 year old. Or someone who does
not speak English natively.

Either that or, knowing how these things have been rolling aroud the planning
and NIMBY protest camps for years, perhaps the author gave it precisely the
right amount of effort and attention to detail it deserved.

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quokwok
"Tidal Lagoon Swansea Bay is thought to be seeking a guaranteed subsidised
price of about £168 for every megawatt-hour (MWh) of electricity it generates
over a 35-year period – almost four times the current market price of power."
[http://www.telegraph.co.uk/finance/newsbysector/energy/11426...](http://www.telegraph.co.uk/finance/newsbysector/energy/11426748/Swansea-
Bay-tidal-lagoon-appalling-value-for-money-says-Citizens-Advice.html)

~~~
Alphasite_
I'd assume that 35 years of inflation needs to be factored in as well, at 2%
that would half subsidy by that point. Also, there is an inherent cost to
green power, if it was cheap power companies would flock to build them of
their own accord, but of course they dont, so the government has to subside
them.

~~~
quokwok
If something has negative externalities, the solution is to tax the
externality. E.g. a carbon tax will raise the price of fossil-fuel energy,
which will make some green energy projects worth building. That's it -- job
done.

Subsidising "good" projects is instead of taxing bad projects is the wrong way
to do it, because the government has to evaluate every project proposal to
figure out which projects should be subsidised. Whereas a carbon tax does it
for you; all the government needs to figure out is the cost of carbon, and the
market takes care of the rest.

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porker
How are they going to stop the lagoon from silting up and becoming shallower,
short of dredging it regularly?

~~~
monk_e_boy
Multiple pools. When the silted one is empty at low tide, use the water from
the other pools to wash the silt out.

