Solar radiation correlations for the Athens, Greece, area

In the present study, correlations of the solar radiation for the Athens area are provided, based on hourly measurements over the period 1955–1980. These correlations are of two kinds: The first, which provide the average total radiation incident on a horizontal surface in terms of hour, day, and month of the typical year, is suitable for solar energy collection applications. The correlations of the second kind provide the maximum radiation and are suitable for use in the design of air-conditioning installations or other applications requiring knowledge of maximum values. The correlations of this kind are based on the calculation of the solar constants A, B, and C, i.e. the “apparent solar irradiation at zero air mass,” the “atmospheric extinction coefficient,” and the “diffuse radiation factor,” respectively. These solar constants permit the calculation of the maximum direct normal radiation and of the maximum diffuse radiation as well as of the total radiation on surfaces of various orientations and inclinations. The solar heat gain through fenestration of various orientations (needed in air-conditioning applications) is calculated, as an example of the applications of the solar constants A, B, and C.