Correlating clearness index with cloud cover and other meteorological parameters for forecasting the global solar radiation over Morocco

In this study, new correlations between clearness index and cloud cover without and/or with other meteorological parameters were proposed for estimating the monthly average daily global solar radiation (MADGSR) on a horizontal surface. By using a long-term of continuously observed meteorological data at fourteen cities over Morocco, seventeen new correlation models were established, evaluated and compared with the other seven cloud-based models selected from the literature. The statistical analysis was done based on the coefficient of determination (R²), mean bias error (MBE), mean square error (MSE), root mean square error (RMSE), standard deviation (σ) and performance score (φ). Results revealed that the new proposed model, which combines the clearness index with the cloud cover and all other meteorological parameters, has a good prediction level of the MADGSR for the considered Moroccan cities. The accuracy of the newly developed model may recommend it to be employed in the future design and assessment of the performance of different solar energy applications in Morocco and in other locations with similar climatic conditions.