How efficient are wind turbines?

Wind turbines start operating at wind speeds of 4 to 5 metres per second and reach maximum power output at around 15 metres/second. At very high wind speeds, i.e. gale force winds, (25 metres/second) wind turbines shut down. A modern wind turbine produces electricity 70-85% of the time, but it generates different outputs depending on the wind speed.

Over the course of a year, it will typically generate about 30% of the theoretical maximum output (higher offshore). This is known as its capacity factor. The capacity factor of conventional power stations is on average 50%. Because of stoppages for maintenance or breakdowns, no power plant generates power for 100% of the time.