Comparison of calculated and measured values of total radiation on tilted surfaces in Dhahran, Saudi Arabia

Abstract

The total radiation data measured at Dhahran (lat. 26°18′N, long. 50°08′E), Saudi Arabia, on a surface inclined at 26° from the horizontal for the period March 1984 to April 1985 was used to test three models for calculation of total radiation on inclined surfaces. These models are one isotropic model and two anisotropic models. The total and diffuse radiation measured on a horizontal surface were used when calculating with these models. The above models were compared on the basis of the statistical error tests using the root mean square error (RMSE) and the mean bias error (MBE). The RMSE varied between 0.399% and 5.578%. Our results were compared with similar calculation for Woodbridge, Ontario, Canada (lat. 43.8°N). The comparison showed that the choice of one or another model is location, inclination of the surface and time dependent. For Woodbridge the anisotropic models Klucher and Hay were found to be more accurate than the isotropic model. The present study shows that, for hot-arid areas, the isotropic model is more accurate for tilt angle values around the latitude of the location.