On a universal model for the prediction of the daily global solar radiation

A model to predict the mean expected daily global solar radiation, H(n) on a day n, at a site with latitude phi is proposed. The model is based on two cosine functions. A regression analysis taking into account the mean measured values H-m.meas(n) obtained from SoDa database for 42 sites in the Northern Hemisphere resulted in a set of mathematical expressions of split form to predict H(n). The parameters of the two cosine model for 0 degrees < phi < 23 degrees are obtained by regression analysis using a sum of 3-8 Gaussian functions, while for 23 degrees < phi < 71 degrees the two cosine model parameters are expressed by a sum of exponential functions or the product of an exponential and a cosine function. The main equation of the model and the set of parametric expressions provide H(n) for any phi on Earth. Validation results of this model are provided along with the statistical estimators NMBE, NRMSE and t-statistic in comparison to the corresponding values from three databases of NASA, SoDa and the measured values from ground stations provided in Meteonorm. (C) 2016 Elsevier Ltd. All rights reserved.