Abstract
Solar radiation data are available for many locations on an hourly
basis. Simulation studies of solar energy systems have generally
used these hourly values to estimate long-term annual performance,
although solar radiation can exhibit wide variations during an hour.
Variations in solar radiation during an hour, such as on a minute
basis, could result in inaccurate performance estimates for systems
that respond quickly and non-linearly to solar radiation. In addition,
diffuse fraction regressions and cumulative frequency distribution
curves have been developed using hourly data and the accuracy of
these regressions when applied to short-term radiation has not been
established. The purpose of this research is to investigate the inaccuracies
caused by using hourly rather than short-term (i.e., minute and 3
min) radiation data on the estimated performance of solar energy
systems. The inaccuracies are determined by examination of the frequency
distribution and diffuse fraction relationships for short-term solar
radiation data as compared to existing regressions and by comparing
calculated radiation on tilted surfaces and utilizability based on
hourly and short-term radiation data.
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