Abstract: The present disclosure relates to methods (100, 200) for controlling and operating wind turbines (10). More particularly, the present disclosure relates to methods and systems for determining a surface condition of one or more wind turbine blades (22) of a wind turbine (10). a method comprises rotating the wind turbine rotor (18) under the influence of a wind in predetermined rotation conditions, wherein the predetermined rotation conditions include at least a predetermined pitch angle (252) of the additional wind turbine blades (222, 223). The method further comprises determining a current value of one or more parameters of the wind turbine (10) when rotating in the predetermined rotation conditions and comparing the current value of the one or more parameters of the wind turbine with one or more reference values (37) to determine the surface condition of the wind turbine blades (22).

Abstract: A method for operating a horizontal axis wind turbine is provided, the wind turbine including: a rotor including a rotor blade, wherein the rotor is rotatably coupled to a nacelle, and the rotor is rotatable about a horizontal rotor axis extending through the nacelle, and the nacelle is rotatably coupled to a tower, the nacelle rotatable in a yaw plane about a yaw axis. The method includes determining a wind direction; determining a yaw angle setting, wherein the yaw angle setting deviates from an alignment of the rotor axis and the wind direction in the yaw plane; yawing the nacelle to the yaw angle setting; and operating the wind turbine for example to generate electricity.

Abstract: According to the present disclosure, a method of operating a wind turbine including operating the wind turbine in a noise reduction mode based on at least one set point of a wind turbine parameter such that noise produced by said wind turbine remains below a predefined noise emission level, obtaining an actual air density related value, and applying a correction factor to the at least one set point of a wind turbine parameter is provided. The correction factor is determined in dependence of said actual air density related value.

Abstract: A method for operating a horizontal axis wind turbine is provided, the wind turbine including: a rotor including a rotor blade, wherein the rotor is rotatably coupled to a nacelle, and the rotor is rotatable about a horizontal rotor axis extending through the nacelle, and the nacelle is rotatably coupled to a tower, the nacelle rotatable in a yaw plane about a yaw axis. The method includes determining a wind direction; determining a yaw angle setting, wherein the yaw angle setting deviates from an alignment of the rotor axis and the wind direction in the yaw plane; yawing the nacelle to the yaw angle setting; and operating the wind turbine for example to generate electricity.

Abstract: According to the present disclosure, a method of operating a wind turbine including operating the wind turbine in a noise reduction mode based on at least one set point of a wind turbine parameter such that noise produced by said wind turbine remains below a predefined noise emission level, obtaining an actual air density related value, and applying a correction factor to the at least one set point of a wind turbine parameter is provided. The correction factor is determined in dependence of said actual air density related value.