NCPA - National Center for Policy Analysis

How Efficient Are Wind Farms?

May 3, 2011

Wind farms are much less efficient than claimed, producing below 10 percent of capacity for more than a third of the time, according to a new report.  The analysis also suggested output was low during the times of highest demand, says BBC News.

  • The research, carried out by Stuart Young Consulting for the John Muir Trust, analyzed electricity generated from UK wind farms between November 2008 and December 2010.
  • Statements made by the wind industry and government agencies commonly assert that wind turbines will generate on average 30 percent of their rated capacity over a year.
  • But the research found wind generation was below 20 percent of capacity more than half the time and below 10 percent of capacity over one third of the time.

The study also challenged industry claims that periods of widespread low wind were "infrequent."

  • The average frequency and duration of a "low wind event" was once every 6.38 days for 4.93 hours.
  • During each of the four highest peak demands of 2010, wind output reached just 4.72 percent, 5.51 percent, 2.59 percent and 2.51 percent of capacity, according to the analysis.
  • It concluded wind behaves in a "quite different manner" from that suggested by average output figures or wind speed records.

Source: "Wind Farm Efficiency Queried by John Muir Trust Study," BBC News, April 6, 2011.  Stuart Young, "Analysis of UK Wind Power Generation," John Muir Trust, March 2011.

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