As installed wind turbine energy generation capacity increases, the interest in optimizing these wind turbines increases as well. The optimal operating points for the power and speed control of the turbines depends on a mapping to the power conversion ratio (Cp) from tip speed ratio and blade pitch angles. This mapping changes slowly with time, which can lead to a non-optimal operation of the turbine with time. Another issue is quality of the initial mapping. It might be correct but it can be uncertain. This paper introduces a scheme to estimate this power conversion ratio. The estimated values can subsequently be used to calculate a new operating point. The estimation is based on an optimal unknown input observer.