On 19 December 2012 the Renewable Energy Foundation published a new peer-reviewed study showing that the economic life of onshore wind turbines is between 10 and 15 years, not the 20 to 25 years the wind industry and government assumes. Statistical study of windframs in both the UK and in Denmark show that the average load factor of wind farms declines substantially as they get older, probably due to wear and tear. This decline in performance means that it is rarely economic to operate wind farms for more than 12 to 15 years. As a consequence, the lifetime cost per unit (MWh) of electricity generated by wind power will be considerably higher than official estimates.
The evidence also suggests that offshore windfarms decline faster than onshore ones; that progressively worse onshore sites are being developed; and that larger wind farms have a systematically worse performance than smaller ones.