Hourly values of solar irradiation in clear skies

Abstract

Hourly values of global solar irradiation in clear skies are determined as a function of solar elevation using empirical parameters derived from the measurements of radiation in Zagreb (φ = 45.828° N, λ= 15.992° E) in the period between 1960 and 1985. The estimation was performed on the 15^th of every month for geographical latitudes between 41° and 46° N. By means of the well known procedure the global solar radiation is then divided into the direct and diffuse solar radiation and calculated for a south-facing surface inclined at 35°. A possibility of taking into consideration the influence of clouded sky on the decrease in the clear-sky solar irradiation is also presented.