Solar irradiation polygon concept and application in Turkey

Classical approaches based on the Angstrom equation for expressing the sola r global irradiation in terms of sunshine durations are abundant in the lit erature. However, all of them include mostly linear and to a lesser extent nonlinear relationships between these variables. The parameters in these re lationships are determined invariably by the least squares technique leadin g to regression lines or curves as models. None of these models provides wi thin year variations in thr parameters and they are all very rigid in the a pplication yielding to a single solar global irradiation estimate for a giv en sunshine duration value. This paper presents a solar irradiance polygon (SIP) concept for evaluating both qualitatively and quantitatively the with in year variations in the solar energy variables. On the basis of Sips, mon thly, seasonal and annual parameters of the classical Angstrom equation are calculated. (C) 1999 Elsevier Science Ltd. All rights reserved.