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CT: The Betz limit is the theoretical maximum efficiency for a wind turbine, conjectured by German physicist Albert Betz in 1919. Betz concluded that this value is 59.3%, meaning that at most only 59.3% of the kinetic energy from wind can be used to spin the turbine and generate electricity. In reality, turbines cannot reach the Betz limit, and common efficiencies are in the 35-45% range.
Wind turbines work by slowing down passing wind in order to extract energy. If a wind turbine was 100% efficient, then all of the wind would have to stop completely upon contact with the turbine—which isn’t possible by looking at a wind turbine (figure 1). 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.
S: EnEd (last access: 21 January 2026)
N: 1. The term “Betz limit” is an eponym named after the German physicist Albert Betz (1885–1968), who first described it in 1919.
– Betz (pn): Albert Betz, a German physicist (1885-1968), is best known for his significant contributions to wind turbine technology. He is the author of the famous Betz limit, a law that establishes the theoretical maximum efficiency that can be achieved by a wind sensor.
– limit (n): c. 1400, “boundary, frontier,” from Old French limite “a boundary,” from Latin limitem (nominative limes) “a boundary, limit, border, embankment between fields,” which is probably related to limen “threshold,” and possibly from the base of limus “transverse, oblique,” which is of uncertain origin. Originally of territory; general sense from early 15c. Colloquial sense of “the very extreme, the greatest degree imaginable” is from 1904.
2. The maximum efficiency of an ideal wind turbine rotor is well known as the ‘Betz limit’, named after the German scientist that formulated this maximum in 1920. In 1976, Bergey showed that the British scientist Lanchester derived the same maximum already in 1915. Betz and Lanchester were representatives of leading aerodynamic research schools in the first decades of the previous century. A study of early Russian publications on rotor aerodynamics now shows that the Russian aerodynamic school also produced the same result; its leader Joukowsky derived the maximum efficiency for an ideal wind turbine in 1920, the same year as Betz did. Consequently, in order to honour all, this ideal efficiency should be named the ‘Lanchester-Betz-Joukowsky limit’ in scientific writing. The well-established and convenient name Betz limit is to be considered an easy abbreviation of this full name. Copyright © 2007 John Wiley & Sons, Ltd.
3. Aerodynamics and Theory of Gases; Wind Energy: Betz limit, Betz coefficient.
- The maximum fraction of the power in the wind that can theoretically be extracted by a wind turbine, usually given as 16/27 (about 59%).
4. Energy Transformation; Electric Rotary Machines – Types; Aerodynamics and Theory of Gases; Wind Energy: Betz law, Betz’s formula, Betz formula
- The theoretical maximum amount of the wind energy that can be extracted by a machine [which] was calculated to be 59,3 percent by A. Betz.
- In practice, the efficiency limit is approximately 40 percent.
S: 1. Etymonline (last access: 21 January 2026); GJN (last access: 20 January 2026). 2. OLW (last access: 21 January 2026). 3 & 4. TERMIUM PLUS – https://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-fra.html?lang=fra&i=1&srchtxt=Betz+limit&codom2nd_wet=1#resultrecs, https://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-fra.html?lang=fra&i=1&srchtxt=Betz+law&codom2nd_wet=1#resultrecs (last access: 21 January 2026).
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CR: blade, kinetic energy, power in the wind, rotor, wind energy, wind turbine (1), wind turbine (2).
