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.