The Betz limit is the theoretical maximum efficiency for a wind turbine, calculated by German physicist Albert Betz back in 1919 [1]. Betz calculations showed that this value is 59.3%, which allowing at most only 59.3% of the wind kinetic energy to spin the turbine and generate electricity. In reality, turbines cannot reach the Betz law, and common efficiencies are in the 35-45% range [2,3].
Why 59.3%?
Wind turbines work by using wind in order to turn the blaed and also extract the kinetic energy. With 100% efficiency, then all of the wind would have to stop completely upon contact with the turbine—which isn’t physically possible. In order to stop the wind completely, the air wouldn’t move out of the way to the back of the turbine, which would prevent further air from coming in—causing the turbine to stop spinning [2,3]. According to Betz’s law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in the wind. The factor 16/27 (0.593) is known as Betz’s coefficient. Practical utility-scale wind turbines achieve at peak 75–80% of the Betz limit [1].
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References
[1] Wikipedia, URL: https://en.wikipedia.org/wiki/Betz%27s_law
[2] Energy Education
[3] REUK, Betz Limit – Wind [Online], URL: http://www.reuk.co.uk/Betz-Limit.htm
