A COMPARISON OF SEVERAL DIFFUSE SOLAR-RADIATION MODELS FOR GREECE

This paper attempts to test the applicability of existing correlation models to the estimation of diffuse radiation with respect to measured values at a station. There are two types of model: The first type depends on the fraction of monthly average daily diffuse radiation to total solar radiation, K = H(d)BAR/HBAR, as a function of the "clearness index", K(T) = HBAR/H0BAR. The second type expresses the fraction H(d)BAR/HBAR or H(d)BAR/H0BAR as a function of the sunshine fraction nBAR/NBAR. Therefore, it presents statistically based correlations between global radiation and its diffuse component on a horizontal surface and suggests two equations to determine the ratio of diffuse radiation to total radiation received on a horizontal surface. The results of these correlation equations are compared with other accepted equations.