This paper proposes a method to evaluate the available solar energy according to different types of sky (clear sky, moderately covered sky and covered sky). Four semi-empirical models for the estimation of solar radiation (Link Cloudiness Factor (LCF), Perrin-Brichambaut (PB), Ghouard (GD), Bird Hulstrom (BH)) have been used to predict the solar radiation according to the sky conditions. An analysis of the influence of the seasonal variation on the quality of available solar energy potential is carried out. This study focused on the two seasons (dry seasons and rainy season) identified for the Nouakchott site. The proposed approach was used and validated for the case of the Nouakchott site, using the solar radiation measured data over the period of one year. Results of the study showed three cases: The first was the clear sky case which includes two cases one is during the rainy season, where the model of the LCF is the best with Normalized Mean Square Error NMSE (0.073) and Correlation Coefficient R (0.975), and the other was during the dry season, where the model of BH was most suitable with NMSE (0.069) and R (0.973). The second case was the moderately covered sky, where the GD model indicated was the best model during the dry season whereas BH showed the best results with NMSE (0.242) and R (0.911) during the rainy season. The third case is the covered sky, where GD model with NMSE (0.880) and R (0.831) in dry season and PB model with NMSE (0.615) and R (0.831) in the rainy season were the most adapted ones.
Key words: Solar energy, stat of sky, prediction, solar radiation, clearness index.
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