We have all seen stationary wind turbines on a calm day, and even on some very windy days. It’s a fact that wind farms only produce about a quarter to a third of the electricity that they would if wind speeds were ideal at all times and no maintenance was ever necessary. However this does not mean wind farms do not make a significant contribution to electricity supplies. It is rare for the wind to stop blowing across the whole country, so even when one wind farm is not producing, others may be operating at full capacity.
Before a wind farm is built the average wind speeds for the site are measured. The developers would not go ahead if a significant amount of electricity could not be generated and sold. Fortunately for the UK, we have some of the best wind power resources in Europe. Wind now provides more electricity than hydro power in Scotland - in 2011 it supplied around 18% of the amount of electricity consumed. Five years earlier the figure was just 5%. More details are available here.
If a wind turbine or power station operates at full capacity all day every day, its ‘load factor’ is 100%. Because wind speeds vary, the average load factor for UK wind farms in 2009 was 27%. This may sound low, but it is worth noting that even fossil fuel burning power stations and nuclear power do not operate at full capacity all of the time; they need maintenance and they have to respond to electricity demand. Some coal fired power stations are operated for restricted hours to limit the pollution they cause. The ‘load factor’ for coal-fired power stations in 2009 was 39%, for gas-fired power stations it was 63% and for nuclear it was 66%. More details are available here on page 123.
So next time you see a wind turbine sitting idle, don’t assume the wind farm is not effective at generating electricity.
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