Why Do Wind Turbines (Usually) Have 3 Blades?

For the last eight years I have been working in the wind energy industry, designing wind turbine blades. A lot of people I talk to ask me questions about wind energy, and by far the most common of these is: “why do wind turbines have three blades?”

Nearly all modern wind turbines look roughly like this. (Rosemary Barnes)

It is an interesting question because there is actually a lot of disagreement amongst engineers about what the reason is. If you ask five…