The coefficient of performance for an ideal wind mill is
UGC NET - 2014,
Answer: D
The maximum coefficient of performance (power coefficient) of an ideal wind mill is 16/27, about 0.593, the Betz limit. It follows from the momentum theory in which the wind speed behind the rotor is one third of the speed in front, so only 16/27 of the wind power can be taken out.
3/8, 5/16 and 2/5 are not values given by the theory, so they are wrong.
The Betz limit holds for any wind turbine in an open stream, and real machines reach only a part of it, since losses in the blades, gearbox and generator reduce the output further.
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