Determining a design load for designing a wind turbine component

A method of designing a wind turbine component, the method comprising:

• for each of a plurality of defined load cases of the wind turbine:
• for each of a plurality of defined values of an operational parameter of the wind turbine:
• simulating operation of the wind turbine at the respective defined operational parameter value for the respective defined load case;
• and
• determining, based on output from the simulation, a characteristic extreme load, for the respective defined load case, experienced by the wind turbine at the respective defined operational parameter value;
• and
• obtaining a combined characteristic extreme load for the respective defined load case using a combining function that depends on the determined characteristic extreme load, and a defined probability of wind turbine operation, at each respective defined operational parameter value;
• determining a design load for extreme loading of the wind turbine based on the plurality of combined characteristic extreme loads for the respective defined load cases;
• and
• designing the wind turbine component in accordance with the determined design load.