Ageing is a fact of life. Just as with conventional forms of power generation, the energy produced by a wind farm gradually decreases over its lifetime, perhaps due to falling availability, aerodynamic performance or conversion efficiency. Understanding these factors is however complicated by the highly variable availability of the wind.This paper reveals the rate of ageing of a national fleet of wind turbines using free public data for the actual and theoretical ideal load factors from the UK's 282 wind farms. Actual load factors are recorded monthly for the period of 2002–2012, covering 1686 farm-years of operation. Ideal load factors are derived from a high resolution wind resource assessment made using NASA data to estimate the hourly wind speed at the location and hub height of each wind farm, accounting for the particular models of turbine installed.By accounting for individual site conditions we confirm that load factors do decline with age, at a similar rate to other rotating machinery. Wind turbines are found to lose 1.6 ± 0.2% of their output per year, with average load factors declining from 28.5% when new to 21% at age 19. This trend is consistent for different generations of turbine design and individual wind farms. This level of degradation reduces a wind farm's output by 12% over a twenty year lifetime, increasing the levelised cost of electricity by 9%

This paper evaluates the impact of intermittent wind generation on hourly equilibrium prices and output, using data on expected wind generation capacity and demand ,for 2020. Hourly wind data for the period 1994-2005 are used to obtain wind output generation profiles for thirty regions (onshore and offshore) across Great Britain. Matching the wind profiles for each month to the actual hourly demand (scaled to possible 2020 values),we find that the volatility of prices will increase, and that there is significant year-to-year variation in generators’ profits. In the presence of significant market power (the equivalent of two symmetric firms owning fossil-fuelled capacity, rather than six), the level of prices more than doubled, and their volatility increased. Our results lend support to the theoretical findings of Twomey,and Neuhoff (2005), showing that the impact of market power should be expected to raise revenues less for wind than for thermal generators. JEL Codes: D43, L13, L94, Q41, Q42 Keywords: Electricity markets, Intermittent Output, Imperfect Competition, Wind generation, Generation Mix.