Q: What is the efficiency of wind power?
The power efficiency of the rotor is defined as a fraction of the entire accessible power that the wind blades are able to convert into useful energy. A wind turbine is not able to convert 100 percent of the energy from the wind because it is limited by the so-called Betz law.
The Betz law says that at most 59.3 percent of the total wind energy can be extracted. The concept was developed in 1919 by a physicist Albert Betz who formed a theory about the maximal possible extraction of energy through the use of wind turbines. The percentile factor of 0.593 is called Betz limit or Betz coefficient.
A wind turbine should preferably operate as close as possible to the Betz coefficient.
To illustrate the nature of the Betz limit, it is sufficient to note that in order to extract 100 percent of the kinetic energy, the blades would have to stop the wind completely. This would require all the swept area (the area covered by the spinning blades) to be of a disk-like, solid shape. However, in that particular scenario, the blades would not turn and the wind would flow around the turbine. There would thus be no energy conversion in such an extreme scenario.
Betz coefficient is significant because it is used to calculate power output from the wind turbine.