Correlations for Estimation of Solar Radiation on Horizontal Surfaces

In this study, variation of the solar radiation over horizontal surfaces for clear-sky atmospheres was predicted and compared with measurements carried out in Erzurum, Turkey (latitude: 39.55, longitude: 41.16, and altitude: 1869 m). Hottel's clear-sky model was used in calculations of solar radiation on horizontal surfaces for clear-sky atmospheres. The results show that the model calculations are reasonably consistent with the measured data. It is recommended that Hottel's clear-sky model can be used for solar radiation calculations in Erzurum. Also, correlation equations giving monthly averages of clear-sky and global solar radiation on horizontal surfaces have been developed. In order to indicate the performance of the correlation equations, the relative percentage error, correlation coefficient, mean percentage error, mean bias error, and root-mean-square-error methods were used.