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.
2005 Elsevier Ltd. All rights reserved
