NOVELTY - The method involves calculating (S8) hourly electric power generation efficiency of a solar power generation device. The correction completed hourly electric power generation efficiency is calculated by correcting power generation efficiency with correction coefficient corresponding to difference of reference air temperature. The hourly electric power generation amount of solar power generation device is obtained by multiplying amount of hourly global solar radiations and maximum output of power generation device by corrected power generation efficiency.    USE - Electric-power-generation-amount prediction method in photovoltaic power generation.    ADVANTAGE - The electric power generation amount in photovoltaic power generation can be estimated with high precision, without measuring sunshine intensity, air temperature, and electric power generation amount in real time. The estimated electric power generation amount can respond rapidly and easily, even during the change of weather report. The presence or absence of detection of failure of solar power generation device and output suppression can be judged easily.    DETAILED DESCRIPTION - The electric power generation efficiency pattern intrinsic to the solar power generation device which shows correlation between hourly electric power generation efficiency, and the approximation formula showing the electric power generation efficiency pattern are calculated. The amount of hourly global solar radiations from the dawn in the installation place of the solar power generation device to sunset is calculated using the performance value of the air transmittance of the installation place. The sunshine correction factor is calculated using the weather function, and the influence which the air transmittance attenuate with clouds or humidity using the sunshine correction factor is adjusted, while calculating the weather function showing correlation of humidity and percentage of possible sunshine from the weather performance of the past in the installation place. The hourly electric power generation efficiency of the solar power generation device is calculated from the amount of accumulation global solar radiations using the approximation formula showing the electric power generation efficiency pattern, after computing amount of accumulation global solar radiations. An INDEPENDENT CLAIM is included for an electric-power-generation-amount prediction apparatus in the photovoltaic power generation.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow diagram illustrating the operation of the electric-powergeneration-amount prediction apparatus. (Drawing includes non-English language text)    Step for acquiring data of the day which estimates electric power generation amount (S1)    Step for estimating future electric power generation amount (S2)    Step for reading nearby observatory of electric power generation place from observatory information preservation unit (S3)    Step for obtaining electric power generation place and weather function corresponding to electric power generation day saved in the weather function preservation unit (S4)    Step for calculating hourly electric power generation efficiency (S8)