Why do windmills typically have 4 blades, yet all modern wind turbines have 3?

Question

Why do windmills typically have 4 blades, yet all modern wind turbines have 3?

In: 9124

Answer 1

The top answer does leave out one of the most important aspects of Windmills: the [tip-speed ratio](https://en.m.wikipedia.org/wiki/Tip-speed_ratio)

It determines the ratio between the tangential speed of the tip of the windmill wing and the wind speed.
Generally the higher the tip-speed ratio, [the less Blades a Wind Turbine has](https://upload.wikimedia.org/wikipedia/de/9/98/Schnelllaufzahl.png)

Windmills heaving three blades is a balance between rotational Speed, noise, cost, efficiency, etc. (Slower Windmills with more Blades would need bigger gearboxes –> more cost; faster Windmills would be louder and more instable –> more expensive materials and more difficulty with regulations.)

One single answer is often not possible with such complex Topics.

Edit: The size of the Turbine is also important because the tip-speed is dependent on it, effecting the tip-speed ratio (older Windmills are smaller than Modern Wind Turbines –> less blades on modern Turbines)

Answer 2

The top answer does leave out one of the most important aspects of Windmills: the [tip-speed ratio](https://en.m.wikipedia.org/wiki/Tip-speed_ratio)

It determines the ratio between the tangential speed of the tip of the windmill wing and the wind speed.
Generally the higher the tip-speed ratio, [the less Blades a Wind Turbine has](https://upload.wikimedia.org/wikipedia/de/9/98/Schnelllaufzahl.png)

Windmills heaving three blades is a balance between rotational Speed, noise, cost, efficiency, etc. (Slower Windmills with more Blades would need bigger gearboxes –> more cost; faster Windmills would be louder and more instable –> more expensive materials and more difficulty with regulations.)

One single answer is often not possible with such complex Topics.

Edit: The size of the Turbine is also important because the tip-speed is dependent on it, effecting the tip-speed ratio (older Windmills are smaller than Modern Wind Turbines –> less blades on modern Turbines)