CRITICAL ANALYSIS AND PERFORMANCE ASSESSMENT OF CLEAR-SKY SOLAR IRRADIANCE MODELS USING THEORETICAL AND MEASURED DATA

Eleven clear sky irradiance models have been selected for this analysi s. All predict the beam, diffuse, and global radiation on a horizontal surface. Three types of analyses are made in order to test the validi ty of the models, their limitations, and their performance for standar d or real conditions. First, a detailed analysis of the main equations of the models is performed. It is shown that atmospheric effects are not always correctly modeled. The modeling of water vapor absorption, and more importantly of aerosol extinction mostly conditions the overa ll model accuracy. Second, the performance of each model is statistica lly evaluated by comparison with a benchmark constituted by the predic tions of three sophisticated spectral codes. Third, real life performa nce is evaluated by comparison with a large number of measured data fr om seven sites around the world, encompassing a wide range of atmosphe ric conditions. The more physical models are found to be generally of higher accuracy and greater flexibility than empirical models.