Weak Wind

I've previously reported one major drawback to using solar or wind power for electric generation: both such sources are highly intermittent (down to zero for solar at night), and national grids can accommodate only about 20 percent from variable sources--after that, the fluctuations begin to tell. (There are plenty of other problems with wind energy, of course.)

Turns out I was underestimating the problem: "Wind farms are much less efficient than claimed, producing below 10% of capacity for more than a third of the time." According to a recent report by the John Muir Trust, five assertions made regularly by the wind industry and Scottish Government are false:

1. 'Wind turbines will generate on average 30% of their rated capacity over a year'
In fact, the 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.

2. 'The wind is always blowing somewhere'
On 124 separate occasions from November 2008 to December 2010, the total generation from the windfarms metered by National Grid was less than 20MW (a fraction of the 450MW expected from a capacity in excess of 1600 MW). These periods of low wind lasted an average of 4.5 hours.

3. 'Periods of widespread low wind are infrequent.'
Actually, low wind occurred every six days throughout the 26-month study period. The report finds that the average frequency and duration of a low wind event of 20MW or less between November 2008 and December 2010 was once every 6.38 days for a period of 4.93 hours.

4. 'The probability of very low wind output coinciding with peak electricity demand is slight.'
At each of the four highest peak demand points of 2010, wind output was extremely low at 4.72%, 5.51%, 2.59% and 2.51% of capacity at peak demand.

5. 'Pumped storage hydro can fill the generation gap during prolonged low wind periods.'
The entire pumped storage hydro capacity in the UK can provide up to 2788MW for only 5 hours then it drops to 1060MW, and finally runs out of water after 22 hours.

These findings are consistent with recent anecdotal evidence that about one quarter of the windmills at California's Tehachapi pass farm were inoperative, possibly because of maintenance issues, even on a windy day.

It may be an exaggeration to say that "wind farms are totally useless." But wind is comparatively expensive and unreliable. Other than that, Mrs Lincoln. . .

(via Coyote Blog via reader Warren)