The number of blades of a wind turbine, like many other design issues, is a compromise. Because each blade disrupts the air for the next blade, you should use as few blades as possible to maximise efficiency.
If you've ever seen a wind turbine start up, you'll notice that the blades begin rotating slowly at first and then begin accelerating faster and faster. This is due to the blades' aerodynamic design.
The greater the number of blades on a wind turbine, the greater the torque (the force that causes rotation) and the slower the rotational speed (due to increasing drag produced by wind flow resistance). However, turbines used to generate power must operate at high speeds and do not require considerable thrust. As a result, the less the number of blades, the better adapted the system is for power generation.
ONE BLADED TURBINE :
In theory, the most aerodynamically efficient arrangement is a one-bladed turbine. However, due to stability issues, it is not very practical.
TWO BLADED TURBINE :
Turbines with two blades are the next best option, however they suffer from a wobbling effect akin to gyroscopic precession.(When an external torque is applied to a spinning item, its axis describes a cone in space, a process known as gyroscopic precession).
In the case of a two-bladed turbine, because a wind turbine must always face towards the wind, the blades must change vertically as the wind direction changes.Once in a spin, a two-bladed turbine will go totally vertical and completely horizontal.This will cause vibrations.
THREE BLADED TURBINE :
A turbine with three blades, on the other hand, has very little vibration or chatter. This is because when one blade is horizontal, the two other blades counter-balance its resistance to yaw force. As a result, a three-bladed turbine offers the ideal mix of high rotating speed and low stress.
The higher the cost of production, the more blades you put to the system. This may sound apparent, but when it comes to producing electricity from a turbine, every pound counts, and switching to a four turbine system will cost more to construct.
