Evaluation of long-cycle fluctuation of spatial average insolation in electric utility service area

High penetration photovoltaic power generation system (PVS) would cause some negative impacts on the stable operation of electric power system. On the other hand, when PVSs are widely dispersed, the total power output fluctuation would be smoothed. In order to evaluate the spatial average insolation fluctuation by using the insolation data observed at the limited number of points, we have developed the method to take the smoothing-effect around the observation point into account. Then, by using the insolation data observed at 61 points in the Chubu region in Japan, this study statistically evaluated the long-cycle fluctuation of the spatial average insolation. As the results, the absolute value of the maximum fluctuation width (MFW) of ensemble average insolation calculated with 120 min width window ranges mainly between 200 and 300 W/m
²
, while it is larger than 400 W/m
²
in 6 days (1.7%). The results suggest that the reliable forecast method of spatial average insolation is needed to mitigate the impact of total power output change due to the insolation change of 400 W/m
²
in 120 min.