The purpose of this research is to obtain the optimum sampling period for evaluating solar photovoltaic generation beforehand. For this purpose, the solar radiation was measured over 1 year at the once per a week. The effect of the sampling period on the integral error of amount of solar radiation was analyzed, and the fractal analysis of the solar radiation was carried out. As a result, the following issues were clarified. Er=0.0117t and t=0.00201Qa+1.934 were obtained as a relational expressions of the sampling period (t) and the integral error (Er) in amount of solar radiation, and of the amount of solar radiation (Qa) and the sampling period (t). Upper limit in the optimum sampling period was the 236 seconds, when allowed integral error of amount of solar radiation was 3%.
