On Mon, 28 Mar 2011 17:43:14 +0100, Ronald Raygun
wrote:

The Natural Philosopher wrote:

Ronald Raygun wrote:

I agree that the 7% figure for wind is impressive, especially as an
annual
total, i.e. as a long term average. It implies the peak fraction must be
a lot higher, and partly that must be due to the fact that there is a lot
of fossil in use anyway, capable of being backed out at the drop of a hat
when the wind is blowing well enough to take over a decent share of the
load.

Indeed. Coal mostly. some gas.

But realistically, how much fuel do you save if you shut a coal plant
down to idle for a few days while the wind blows... the efficiency is
utter crap when you do that.

I don't think you'd want to shut one right down to idle. You'd simply want
to throttle it (or if necessary several of them) back a bit, until they
generate as much less electric power as the windmills generate more.

Essentially the windmills then give you negative carbon emissions as a
result of the coal which is not burnt.

That works for small amounts of wind generation, add a few GW of the
things and it all goes Pete Tong.

Almost without exception, coal gas and nuclear generation is more
efficient when operated at full output. Where design problems restrict
output or there are plant problems, then efficiency can drop off
significantly. For instance one coal fired power station has always
been more expensive to run than another one just a few miles away
built at about the same time. That it can only run at around 90% of
rated output is the main factor in this, what makes it even worse is
this lower efficiency increases cost, which means it is forced to run
on a flexible basis, meaning costs are even higher as the plant wears
out faster and efficiency drops even lower. Some of that flexible
running and the consequent drop in efficiency and increased emissions
can be directly attributable to the unpredictability of wind turbines.


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