THE EFFECT OF CLOUDS ON SOLAR-RADIATION

Measured solar data for Amman (lat 32-degrees-N) were used to compute the empirical constants in the following correlation proposed by Page: H(d)BAR/HBAR = c + d HBAR/H(o)BAR where HBAR, H(d)BAR and H(o)BAR are monthly average daily global, diffuse and extraterrestrial radiation on a horizontal surface, and c and d are empirical constants. The measured solar data were classified into 12 groups of days depending on the ratio S/S(o), where S is the daily number of sunshine hours and S(o) is the day length. The empirical constants c and d were evaluated for each group. The computed values of the constants were used to develop correlations for both constants. Finally, values for c and d were also obtained under clear sky conditions (S/S(o) = 1.0) and under average sky conditions (0.0 < S/S(o) < 1.0). The obtained values of the diffuse radiation component, using these empirical constants, under both sky conditions showed very good agreement.