Computer system for calculating AEP changes of a wind turbine due to identified structural deterioration of the blades and method of maintaining a wind turbine

A computer system suitable for estimating and/or calculating an expected and/or actual change in annual energy production (AEP) of a wind turbine due to identified structural deterioration of blades of the wind turbine, said computer system being arranged to execute the following steps:

• a. loading a dataset representing estimated lift and drag curves at specific radial locations along an original blade of the wind turbine,
• b. building a baseline Blade Element Momentum (BEM) model of the wind turbine based on said estimated lift and drag curves of the original blade and analysing the model to provide a baseline AEP estimation of the wind turbine with original blades,
• c. loading a dataset representing aerodynamic effects of identified structural deteriorations at specific radial locations along each of the blades of the wind turbine,
• d. using the dataset of aerodynamic effects to generate modified lift and drag curves at specific radial locations along each of the blades,
• e. building a modified BEM model of the wind turbine based on the modified lift and drag curves, and
• f. analysing the modified BEM model to get an estimate of the AEP of the wind turbine when the structural deteriorations are taken into account.