In order to maintain the power generation performance of photovoltaic power generation systems, it is common to compare the actual energy yield with the estimated energy yield calculated from the measured solar irradiation in the same location. If there is no on-site measured data of the solar irradiation, it can be estimated from the total global horizontal irradiation measured at 48 JMA sites in Japan. However, in order to use the data which measured at closer points, the sunshine hours measured at 687 AMeDAS sites in addition to JMA sites are also available in Japan. This paper verified the validity of the conversion formula of the hourly integrated sunshine hours into the global horizontal irradiation and updated it with the latest data. Finally, this study propose the model which convert sunshine hours into the global horizontal irradiation: the model can select the optimum coefficient in nationwide and in each solar radiation climatic province which is added in order to maintain simplicity and improve accuracy.
