Validation of the existing models for estimating global solar radiation over Egypt

Solar radiation data are required for many applications and many areas of research. In order to achieve this, several empirical models have been developed to predict the solar radiation in many developing countries like Egypt. The main objective of this study is to review and test the applicability of all models available for computing the monthly average daily global radiation on a horizontal surface, G, in Egypt. The different meteorological data measured at nine stations during the period (1983–2006) were used to calculate the monthly mean values of G over these stations using all available collected models. The collected models (10 models) were compared on the basis of many statistical error tests such as the relative percentage error (e%), the mean percentage error (MPE), mean bias error (MBD), root mean square error (RMSE), t-test and the Nash–Sutcliffe equation (NSE). According to the results, the modified Robaa model (model 8) showed the best estimation of the global solar radiation on a horizontal surface for all nine stations and therefore is recommended for predicting G at any location in Egypt.