The estimation of wind turbine performance over complex terrain is very difficult because the document of standard IEC61400-12 is adapted on flat or slightly complex topography. And the cost of constructing a meteorological mast becomes higher with scaling wind turbine up. Authors have proposed numerical site calibration (NSC) in order to estimate the inflow velocity at the position of wind turbine by using CFD tool for calculating flow field around the site. The present paper shows problems on the procedure of NSC where a commercial nonlinear CFD tool and the method is improved to obtain more accurate result. It is clarified that the wind turbine performance, which is estimated with the calculated wind speed on the meteorological mast by the improved method has a good result for annual energy production.
