Why do wind turbines have three blades? Why not just two?
I will go down in history as the person who asked the last question on AskSam, the NH Public Radio series in which reporter/podcaster Sam Evans-Brown answers listener questions. Sam is leaving radio to become a clean-energy advocate. You can read or listen to his response here. I pretty much knew the answer but Sam went into more detail than I knew and even hunted down the man responsible for the design. Very cool! You want the minimum number possible to reduce construction costs  more blades dont automatically produce more power because of increased drag, despite what many alt-energy tinkerers think  and a single blade would be so lopsided it would unbalance the turbine. Fortunately I have a friend, Earle Rich, who worked on wind turbines in their very earliest days, including Altamont Pass Wind Farm in California, the continents first big wind farm. Here was around when this issue was being thrashed out through design and experimentation and here is his answer:  They simplest answer is that three blades will have uniform thrust on the generator as it yaws into the wind. A two bladed machine, as it turns on the tower to face the wind or tracks downwind, will have maximum resistance to yaw when the blades are parallel to the ground and minimum resistance when they are vertical. This extreme change will cause the tower to periodically torque and this is hard on ground mounting and guy wires, hard on nacelle bearings and other parts.