Comparative study of isotropic and anisotropic sky models to estimate solar radiation incident on tilted surface : a case study for Bhopal, India

The purpose of this study is to compare the different empirical models used for estimation of solar radiation on tilted surface. For this, three isotropic and same number of anisotropic sky models were employed by using average monthly mean value of solar radiation on daily basis at Bhopal, local climatic condition, located in central region of India. The tilt angle was fixed at 23.26°N (latitude of Bhopal). The models results were compared with ground measured data from one sample statistical test. It was found that Hays and Davis model (HD) estimated the highest amount of incident solar radiation in the whole year whereas Badescu model (BA) established the lowest among all isotropic as well as anisotropic models. Finally, Badescu model (BA) was preferred for estimation of solar radiation incident on tilted surface with smallest statistical errors among all models and closed agreement with measured data.