Method for monitoring and assessing power performance changes of a wind turbine

A program product comprising a computer readable medium containing instructions which, when executed by a processor, performs an operation for monitoring and assessing power performance changes of one or more wind turbines of a wind farm, wherein for each wind turbine to be monitored, a group of reference wind turbines is defined, the group of reference wind turbines comprising two or more wind turbines, the operation comprising:

• obtaining locally measured wind speeds at each of the wind turbines while operating the wind turbines during a training period;
• obtaining power performance data for each of the monitored wind turbines, during the training period;
• for each of the monitored wind turbines, generating a transfer function establishing a relationship between the locally measured wind speeds at each of the reference wind turbines and the power performance data for the monitored wind turbines, based on locally measured wind speeds and power performance data obtained during the training period;
• while operating the wind turbines of the wind farm, obtaining locally measured wind speeds at least at the reference wind turbines during a test period, following the training period;
• obtaining power performance data for each of the monitored wind turbines, during the test period;
• for each of the monitored wind turbines, comparing the power performance data obtained during the test period to predicted power performance data obtained by means of the locally measured wind speeds at the corresponding reference wind turbines during the test period and the previously generated transfer function for the monitored wind turbine;
• and
• assessing power performance changes for each of the monitored wind turbines, based on the comparison.