摘要
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<sub>d</sub>) 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<sub>d</sub>. The negative values of mean percentage error MPE % for all models show that for all locations, the proposed correlations slightly overestimate H<sub>d</sub>, and the absolute values of MPE never reach 1.35%. The first, second and third order correlations between the diffuse solar fraction H<sub>d</sub>/H and the clearness index K<sub>t</sub> and between the diffuse transmittance H<sub>d</sub>/H<sub>0</sub> 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<sub>d</sub> show that a first order correlation between H<sub>d</sub>/H and K<sub>t</sub> can be used for estimating H<sub>d</sub> at the present locations with good accuracy. However, second order correlations between Hd/H or H<sub>d</sub>/H<sub>0</sub> and S/S<sub>o</sub> are recommended for estimating H<sub>d</sub> at these locations. The average annual differences between measured and calculated values of diffuse solar energy H<sub>d</sub> on horizontal at selected sites in the present research are discussed.
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<sub>d</sub>) 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<sub>d</sub>. The negative values of mean percentage error MPE % for all models show that for all locations, the proposed correlations slightly overestimate H<sub>d</sub>, and the absolute values of MPE never reach 1.35%. The first, second and third order correlations between the diffuse solar fraction H<sub>d</sub>/H and the clearness index K<sub>t</sub> and between the diffuse transmittance H<sub>d</sub>/H<sub>0</sub> 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<sub>d</sub> show that a first order correlation between H<sub>d</sub>/H and K<sub>t</sub> can be used for estimating H<sub>d</sub> at the present locations with good accuracy. However, second order correlations between Hd/H or H<sub>d</sub>/H<sub>0</sub> and S/S<sub>o</sub> are recommended for estimating H<sub>d</sub> at these locations. The average annual differences between measured and calculated values of diffuse solar energy H<sub>d</sub> on horizontal at selected sites in the present research are discussed.
作者
Samy A. Khalil
Samy A. Khalil(Solar and Space Department, National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Egypt)
