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it is not likely to be blowing at any other within a radius of
roughly
miles. Mathematically this is not a hard
problem to deal with, but to do so you need what the
mathematicians call the two-point correlation functions.
I hope that they exist, but my California expert did not
know of one for California. If they don
t exist today they
are needed to assess the real potential of wind energy.
Because the average output of a wind farm is so much
less than its capacity and is highly variable, there is a
problem; what supplies your electricity when the wind is
not blowing hard, and what do you do with the excess
electricity when it does blow hard? Ideally, technology
would be available to store the excess when the output is
much above the average and release it when the output is
much below average. Unfortunately, affordable large-
scale storage still does not exist at what I call grid scale:
gigawatts of output for days, rather than megawatts for
hours. There is one exception called pumped storage (see
Section
'
). If you have a lake at the bottom of a hill and
another one at the top, you can pump water uphill when
there is lots of wind, and run it downhill through hydro-
electric generators when you need it. Unfortunately, there
are not too many places where pumped storage is possible.
Today, when there is too much wind the system oper-
ators either turn off windmills or turn off something else
and let the wind farms run. When there is too little, they
turn on gas-
.
red plants to make up for the shortage. The
added expense of this kind of operation falls on the users
of electricity, not on the owners of the wind farms. There
is too little effort devoted to grid-scale energy storage,
and until this problem is solved, wind cannot be an effect-
ive and affordable large-scale electricity source.
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