Why do modern wind power turbines only have three blades? If they had six,they'd generate twice the power?

Question

The rotational speed is only dependant on blade stagger angle,load and wind speed. If there were 9,12 or more blades,the power output would rise pro rata & we wouldn't need so many windmills. If it's a question of the wind pressure pushing the support tower over then make it stronger!!

Answer 1

You can only extract a limited amount of energy out of the wind. Adding too many blades cause turbalances that reduces the efficency of the turbine and drives up costs. Look at the screw propeller, it is only 1/6th of a turn.

Answer 2

To frame your question differently, why not have "infinity" blades on the mill in order to get "infinity" times the power output. Of course this can't be the case, or else one windmill would power the earth. So what's the answer to your question? The answer is that there is a compromise to be reached and the best number of blades lies somewhere between 1 and infinity.

But one of the reasons that the optimal number is so low is because at a certain point, too many blades can start to make the wind divert around the mill instead of blowing through it. If there is too much surface area in the circle defined by the blades, wind will re-route around the circle and energy will not be captured.

There is also the fact that turbulence is a power-lower. If there were too many blades, the small amout of turbulence caused by a leading blade would diminish the power generated by a following blade. By having good spacing, the turbulence is blown behind the following blade, and doesn't affect energy capture.

There are several other reasons that have to do with: initial installation costs, maintenance, angular momentum, total mass of structure, and as you mentioned windforce on the tower.

Answer 3

actually speed decreases with number of blades due to drag.
the fewer blades the faster it will spin to cover the swept area. torque increases with "sail" area, for electric generation speed is more important than torque. power is a function of swept area not blade area.

so old water pumps which require high starting torque are an almost solid disc.
there was an experimental one blade wind gerator design, 3 seems to be the best real world compromise

centre for alternative technology wales run excellent wind generator design courses, they may also have some information sheets

Answer 4

this is copied from wikipedia.. please read this article...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.

visit the website and read the whole article
" blade count"

http://en.wikipedia.org/wiki/Wind_turbine#Types_of_wind_turbines

Answer 5

too many blades will distract the energy they are trying to create

Answer 6

They do have turbines with more than 3 blades ! (Tehachapi,Mohave)

Answer 7

they use power them selfs so if there was 6 plades on then thay will use more power then there is no point of them

Answer 8

costs more money that people arent willing to pay