Low Wind Power Output Too Frequent In Britain

A study from the John Muir Trust finds that British wind power output sometimes falls to less than 5% of peak (nameplate) capacity.

The report, Analysis of UK Wind Generation, is the result of detailed analysis of windfarm output in Scotland over a 26-month period between November 2008 to December 2010 using data from the BMRS (Balancing Mechanism Reporting System). It's the first report of its kind, and drew on data freely available to the public. It challenges five common assertions made regularly by wind industry and the Scottish Government:

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.