Estimating Diffuse Solar Radiation from Global Solar Radiation
Abstract
This study considers the estimation of diffuse solar radiation from global solar radiation. This involves investigating the correlation of the fraction of diffuse solar radiation in the global solar radiation (or diffuse fraction) with cloud index. The cloud index is defined in terms of the clear-sky index. Beam solar radiation is sometimes derived from diffuse and global solar radiation. The variation of the ratio of beam to clear-sky radiation with estimated diffuse fraction solar radiation has been investigated for this reason. The results show that the best fit for the plot for fraction of diffuse solar radiation against cloud index and the plot for the ratio of beam to clear-sky radiation against the estimated diffuse fraction are linear and second degree polynomial respectively with respective correlation coefficients of 0.800 and 0.840. The results show that diffuse solar radiation can be estimated from global solar radiation and that beam solar radiation can be calculated from the estimated diffuse radiation.
Keywords
- diffuse solar radiation, Global solar radiation, Beam solar radiation, Cloud index