INVESTIGATION OF MINUTE SOLAR-RADIATION DATA

Simulation studies of solar energy systems have traditionally been performed using hourly data because data for shorter time periods are generally unavailable for extended periods. If simulations using hourly data are to provide accurate results, the variation of radiation within an hour must have a negligible effect on a system's performance. This paper examines minute radiation data from three locations. The distribution of minute data within the hour is found to differ from previously presented distributions of daily radiation in a month. Comparisons of calculated and measured minute radiation on a tilted surface show significant differences which are attributable to inaccurate estimates of the magnitude and distribution of diffuse radiation on a minute basis. Even with the same tilted surface radiation, significant differences in simulated performance using hourly and minute-by-minute data are found to exist for a simple photovoltaic system.