A method for operating a wind turbine generator comprising the steps of: obtaining operating parameters for the wind turbine generator, in which the operating parameters are wind parameters; obtaining operating conditions for the wind turbine generator, in which the operating conditions are current operating or future operating conditions; calculating the amount of fatigue and/or damage caused to the wind turbine generator or components thereof under the operating conditions; calculating a proportion of total life consumed for one of said components under the operating conditions; calculating an equivalent cost per unit time of running one of said components under the operating conditions; comparing the cost per unit time of running one of said components under the operating conditions with a value per unit time of electricity generated by the wind turbine; and adjusting a power output of the wind turbine according to the steps of: increasing the power output when the cost per unit time of running one of said components under the operating conditions is less than said value per unit time of electricity generated by the wind turbine; or reducing the power output when the cost per unit time of running one of said components under the operating conditions is greater than said value per unit time of electricity generated by the wind turbine; in which the step of calculating the fatigue and/or damage includes providing information about the wind turbine generator or components thereof. obtaining operating parameters for the wind turbine generator, in which the operating parameters are wind parameters; obtaining operating conditions for the wind turbine generator, in which the operating conditions are current operating or future operating conditions; calculating the amount of fatigue and/or damage caused to the wind turbine generator or components thereof under the operating conditions; calculating a proportion of total life consumed for one of said components under the operating conditions; calculating an equivalent cost per unit time of running one of said components under the operating conditions; comparing the cost per unit time of running one of said components under the operating conditions with a value per unit time of electricity generated by the wind turbine; and adjusting a power output of the wind turbine according to the steps of: increasing the power output when the cost per unit time of running one of said components under the operating conditions is less than said value per unit time of electricity generated by the wind turbine; or reducing the power output when the cost per unit time of running one of said components under the operating conditions is greater than said value per unit time of electricity generated by the wind turbine; increasing the power output when the cost per unit time of running one of said components under the operating conditions is less than said value per unit time of electricity generated by the wind turbine; or reducing the power output when the cost per unit time of running one of said components under the operating conditions is greater than said value per unit time of electricity generated by the wind turbine; in which the step of calculating the fatigue and/or damage includes providing information about the wind turbine generator or components thereof.