Written question asked by Lord Vinson (Conservative), in the House of Lords. It was answered by Lord Sainsbury of Turville (Labour) on Tuesday, 21 June 2005.

Wind Energy

Question: What was the operational efficiency of fully installed wind turbines on United Kingdom sites as a percentage of their rated output in 2004.

Answer: Information on the operational efficiency (commonly known as the load factor) of onshore wind turbines, as a percentage of their rated output, is published in the Digest of United Kingdom Energy Statistics (DUKES) which is available in the Libraries of the House. In 2003, the last year for which we have published statistics, the averaged load factor across all turbines was 24.1 per cent Load factors vary from year to year and the average for the five years from 1999 to 2003 was 27.4 per cent 2004 figures will be available at the end of July 2005. The calculation of the average load factor includes turbines that were commissioned only part way through the year as well as those which were fully installed. This may depress the overall average load factor slightly. Full details of the load factor calculations are given in paragraph 7.75 of DUKES.

Secondary information