Correlation of monthly-average daily global, diffuse and beam radiation with bright sunshine hours

Abstract Correlations between monthly-average daily radiation and bright sunshine hours for 11 Indian stations have been studied. It is found that the global radiation can be predicted to an accuracy of 0.5% by using the linear relation, G/Gext = a + b (n/N). For diffuse radiation, three different correlations have been tried. For individual applications, any of the three correlations discussed in this paper can be used, but for collective applications, the correlation D/Gext = a + b (n/N) gives better results. Beam radiation is found to be highly dependent upon the local conditions. To develop a single formula for 11 stations involves a large percentage of error. The Hay method [9] is comparable to the equation G/Gext = a + b(n/N) for global radiation, but for diffuse radiation, the equation D/Gext = a + b (n/N) is superior to the Hay method. The correlations for global and diffuse radiation are G/Gext = 0.3156 + 0.4520(n/N) and D/Gext = 0.3616 − 0.2123 (n/N), respectively.