Onshore wind farms in the UK have aged at about the same rate as other kinds of power station. The average wind farm has an annual load factor of about 28% when first commissioned, which declines by about 0.4 percentage points per year. After 15 years, the load factor would have fallen to 23%. This ageing does not appear to have made developers replace their farms early. Forty out of the first forty-five wind farms commissioned in the UK were still operating at this age; four had been repowered. Taking this deterioration into account raises the levelised cost of electricity by around 9% over a 24-year lifespan, discounting at 10 per cent a year. This is a summary of the peer-reviewed paper “How does wind farm performance decline with age?” published in Renewable Energy, vol. 65, pp 775-786, which is available to download from http://tinyurl.com/wind-decline
