It's still useless, essentially. Other than providing jobs for turbine companies and farm developers, its pretended contribution to our energy future is a triumph of wishful symbolism and bad math.
Well, the numbers just got worse. I have always used 30% or even 1/3 as a working factor to reduce nameplate turbine capacity to what it really generates, i.e. a "2 MW" turbine can be counted on to give you on average about .6 MW of real electrons.
But folks who have more history with wind farms are finding out "your results may vary".
A new analysis of wind energy supplied to the UK National Grid in recent years has shown that wind farms produce significantly less electricity than had been thought, and that they cause more problems for the Grid than had been believed.Farmers are in love (mostly) with the idea of a turbine sitting on a corner of their field generating monthly checks and maybe a little electricity. And those of us who drive by can reflect how wonderfully "free" and green that energy is.
The report (28-page PDF/944 KB) was commissioned by conservation charity the John Muir Trust and carried out by consulting engineer Stuart Young. It measured electricity actually metered as being delivered to the National Grid.
In general it tends to be assumed that a wind farm will generate an average of 30 per cent of its maximum capacity over time. However the new study shows that this is actually untrue, with the turbines measured by the Grid turning in performances which were significantly worse:
Average output from wind was 27.18% of metered capacity in 2009, 21.14% in 2010, and 24.08% between November 2008 and December 2010 inclusive.In general, then, one should assume that a wind farm will generate no more than 25 per cent of maximum capacity over time (and indeed this seems set to get worse as new super-large turbines come into service). Even over a year this will be up or down by a few per cent, making planning more difficult.
It gets worse, too, as wind power frequently drops to almost nothing. It tends to do this quite often just when demand is at its early-evening peak:
At each of the four highest peak demands of 2010 wind output was low being respectively 4.72%, 5.51%, 2.59% and 2.51% of capacity at peak demand.
But this is both bad economics and bad fiscal policy.