Efficiency of a wind turbine

 

Applying yesterday's wind power formula to one of the turbines at Watchtree where the swept area is 1735 square metres, I would get a power of 3514kW at a wind speed of 15m/s. Since the rated power output at that speed is 660kW, the efficiency is 660/3514 x 100 = 19%. That is a lot of energy that cannot be captured. As the wind speed goes up, the efficiency will come down because there will be more wind energy going in but the same 660kW output. The data website gives a figure called energy density. It turns out that it is the 660kW divided by the swept area.