By 2020, swapping aging wind turbines with more powerful modern units will have raised annual electricity generation at refurbished sites from 1524 GWh to 8221 GWh. A 2 MW wind turbine coming off the production line with a rotor diameter of 80 metres can generate four to six times as much electricity as the 1 GWh annual yield of a 500 kW wind turbine with a 40 metre rotor built in 1995. This is the fundamental thinking behind wind repowering.