On the importance of relative humidity for prediction of diffuse solar radiation in warm and humid climate of Iran

Abstract

In numerous applications of the solar energy, diffuse solar radiation plays crucial role while their availability in many countries is scarce.Manymodels have been developed to estimate the diffuse solar radiation that each of them is a function of different metrological parameters. The objective of this study is obtaining a model to estimate the diffuse solar radiation in warm and humid climate in Iran and specify the importance of metrological parameters especially relative humidity. Many empirical models in three categories are selected. By using the long-term data for horizontal global solar radiation and sunshine duration and by employing the regression analysis, nine newmodels have been created. Then, by entering two parameters, themonthly mean daily ambient temperature and relative humidity in the empirical models, nine other new models have been developed. Performances of all the models are evaluated by means of different statistical indicators. Obtained results showed adding of the ambient temperature and especially relative humidity parameters cause increasing a few accuracy even though inwarm and humid climate of Iran. The result shown in the two-degree model, in terms of the clearness index and relative sunshine duration, is the best model.