Why most modern wind generators use three blades but not 4 or 5 or more?

Question

Why most modern wind generators use three blades but not 4 or 5 or more?

Answer 1

A wind turbine doesn't produce more energy when there are more blades.  Wind turbines are built with three blades because they give the best results and are more efficient in horizontal axis wind turbines.

There are four blade wind turbines in production however they are not as common as the three blade wind turbines.

There are even single blade wind turbines like this: http://www.residential-wind-power.com/20...

Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional three percent in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner.

Answer 2

cost cutting

Answer 3

When sailboats are racing the lead boat can 'steal' the wind of the following boat making it nearly impossible to pass (although the trailing boat will continue to move but less efficiently).  Using three blades (rather than more) helps insure that each blade finds clean air producing the maximum power per (expensive) blade.  Increasing the blade length increases the power obtained exponentially and wind velocity is also stronger at the higher elevation needed for longer blades.  Still, a great deal of wind passes by unused and wasted.  Because wind turbines are not overall as efficient as power sources that operate at peak performance at all times (winds die down), blade configuration must be optimized (and cost effective) to compete.

Answer 4

You are so right, it seems more logical to use more blades to increase efficiency, perhaps it is a weight issue with all those heavy blades adding weight to the top of a very narrow and tall structure therefore decreasing stability because it is very windy at high elevation in most places.  

Or maybe a reduction of production cost( materials, etc).

Answer 5

Fewer longer blades are more efficient that more shorter blades. There's a trade off between the size of the blades and the number of blades in terms of cost of the wind generator.

Answer 6

A  generator turns harder with excessive weight.