Conclusion
The physics of windmills

The implementation of wind turbine electricity generation must be analysed at many levels.

The first is at blade level, which essentially consists in analysing the external forces acting on it: the force of the wind, the force of air resistance, and the resistance due to generator coupling. The rotational speed of a wind turbine is limited by the appearance of aerodynamic instabilities at the blade tip, i.e. around 350 km/h. This speed corresponds to an optimal wind speed of around 66 km/h. The calculated efficiency is in the order of 25% of the Betz limit, itself equal to 60% of the wind power intercepted by the area swept by the blades. The overall efficiency of large wind turbines is thus in the order of 15%. This optimal value is obtained for wind speeds from 15 to 20 m/s. Typically a 4 MW wind turbine rotates at 20 rpm and has a blade length of around 50 m.

At wind farm...