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Fast-rotating turbines have three rotor blades, while slow-rotating turbines have more.
If you were to build a particularly large wind turbine (rotor diameter greater than 250 m), you would need more than three rotor blades, because with three rotor blades, the rotor tips would approach the speed of sound too close.
But the number of rotor blades has nothing to do with energy transfer. The entire circular area is always taken into account.