Wind power is one of the fastest growing sources of power production in the world today and there is a constant need to increase the power production. Blades are important main component affecting the amount of power production. In addition, there are some sites that the environmental conditions under which wind turbines are operated in Japan are more severe than those in other countries. Therefore there are some blade repair records in spite of wind turbine size. The quantitative power production analysis of before and after blade repairs in Japanese sites are not reported in the literature. This paper shows the analysis results about the comparison of each power curve and annual energy production (AEP) of before and after blade repairs. Uplift in AEP of about 1% is possible through the blade repair. So blades maintenance such as blades repair has proven to be very important.
