Prediction of the Diffuse Solar Energy on Horizontal at Different Selected Locations

The main objective of this paper is to predict the diffuse solar energy on a horizontal surface by using data of global solar energy (H) and diffuse solar energy (H d ) at different selected geographical locations in Saudi Arabia during the period time from 1980 to 2019. The low values of the root mean square error RMSE for all correlations indicated a good agreement between the measured and calculated values of H d . The negative values of mean percentage error MPE % for all models show that for all locations, the proposed correlations slightly overestimate H d , and the absolute values of MPE never reach 1.35%. The first, second and third order correlations between the diffuse solar fraction H d /H and the clearness index K t and between the diffuse transmittance H d /H 0 and the sunshine hours have been proposed for the selected locations using the method of regression analysis. The differences between the measured and calculated values of H d show that a first order correlation between H d /H and K t can be used for estimating H d at the present locations with good accuracy. However, second order correlations between H d /H or H d /H 0 and S/S o are recommended for estimating H d at these locations. The average annual differences between measured and calculated values of diffuse solar energy H d on horizontal at selected sites in the present research are dis-cussed.