Studies on Measurement and Estimation of Solar Radiation : 1st Report, Process and Analysis of Measurements of Solar Radiation at Kitami Institute of Technology

Abstract

Measurements of solar radiation in the past five years from 1978 to 1982 at Kitami Institute of Technology were processed and analyzed, and it was then proved that there was a high correlation between the total solar radiation on a horizontal surface and the direct solar radiation on a normal surface to incidence which were both normalized by dividing by extraterrestrial solar radiation. From the frequency distribution of a number of days which was obtained by grading the daily total radiation on a horizontal surface every 2 MJ/m2d of intensity, a limit value of the direct solar radiation on a normal was introduced in order to define a clear day on which it was possible to use solar energy and a cloudy day on which it was impossible to use solar energy. According to the results of data analysis, the limit value of the direct radiation on a normal, H^-*ND' on the borderline between such clear and cloudy days as above was about 3 MJ/m2d, and the limit value of the total radiation on a horizontal, H*HT, which corresponded to H^-*ND and the ratio of clear days to total days could be obtained as a monthly average over five years.