INVESTIGATION OF MINUTE SOLAR-RADIATION DATA

Simulation studies of solar energy systems have traditionally been per formed using hourly data because data for shorter time periods are gen erally unavailable for extended periods. If simulations using hourly d ata 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 distri bution of minute data within the hour is found to differ from previous ly presented distributions of daily radiation in a month. Comparisons of calculated and measured minute radiation on a tilted surface show s ignificant differences which are attributable to inaccurate estimates of the magnitude and distribution of diffuse radiation on a minute bas is. Even with the same tilted surface radiation, significant differenc es in simulated performance using hourly and minute-by-minute data are found to exist for a simple photovoltaic system.