Method of determining free-flow wind speed for a wind farm

A method for determining free-flow wind speed for a wind farm, comprising:

• a) measuring, for at least one wind turbine of the wind farm, a wind speed in a rotor plane of the at least one turbine, a turbulence intensity in the rotor plane of the at least one turbine, a wind direction in the rotor plane of the at least one turbine, and the power generated by the at least one turbine;
• b) constructing a model for the wind farm connecting at least the free-flow wind speed to the wind speed in the rotor plane of the at least one turbine, to the turbulence intensity in the rotor plane of the at least one turbine to the wind direction in the rotor plane of the at least one turbine and to power generated by the at least one turbine;
• and
• c) determining the free-flow wind speed for the wind farm by use of an ensemble Kalman filter from uncertainties estimated by Monte Carlo draws, applied to the model of the wind farm, and from the measurements of the wind speed in the rotor plane of the at least one turbine, of the turbulence intensity in the rotor plane of the at least one turbine, of the wind direction in the rotor plane of the at least one turbine and of the generated power of the at least one turbine.