Modern horizontal axis wind generators can have one, two or three rotor blades. More than three blades are usually not used. The lower the number of rotor blades, the less material is needed during manufacturing.
Single-bladed rotors must have a counterweight on the opposite side of the rotor. Single-bladed rotors do not have a smooth motion and therefore exhibit a high material stress. Only very few prototypes with one rotor blade exist and it is not expected that this will change soon.
The optimal power coefficient of three-bladed rotors is slightly above that of two-bladed rotors. Three-bladed rotors have an optically smoother operation and hence visually integrate better into the landscape. The mechanical strain is also lower for three-bladed rotors. The advantages of three-bladed rotors compensate for the disadvantage of the higher material demand so that today mainly three-bladed rotors are built.
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