Correction of the ASHRAE clear-sky model parameters based on solar radiation measurements in the Arabic countries

Abstract

In Arabic territories, the ASHRAE clear sky model is commonly used as a basic tool for solar radiation estimation. Unfortunately, this model was developed for the atmospheric condition in the USA, which was quite different from weather conditions of the Arabic territories. The purpose of this study was to revise all parameters of the ASHRAE model under the atmospheric conditions of Arabic countries in an attempt to improve the accuracy of the model. The solar-radiation over horizontal surface calculated by the ASHRAE clear-sky model is compared with measurements form (Brack-Libya, Tulkarm-Palestine and Riyadh- Saudi Arabia) cities in order to test the validity of the ASHRAE clear-sky model parameters (A, B and C).The revised model is tested against statistical analysis based on RMSE, MBE and t-stat. the results showed that the revised model can be a good estimator for the prediction of global solar radiation in Arabic countries with an acceptable agreement to the measured data from meteorological record stations. That performance is a more accurate prediction than those throughout the previous studies. This model presented the unique alternative approach for solar radiation prediction in regard to the locations where there is no availability of some input data for other models. Instantaneous, daily, monthly and yearly solar-radiation on various surfaces such as building walls and flat-plate solar collectors can then be conveniently calculated using the adjusted model for different orientations and inclination angles. The model also allows the beam, diffuse and ground-reflected solar-radiation components to be determined separately.