An Investigation of Modelling Diffuse Solar Radiation Under Tropical Climatic Conditions

Abstract

This paper reports on mathematical formulation and experimental evaluation of global solar radiation components under tropical climate conditions. In the analysis section of this paper, fifteen decomposition models were compared with measured data based on hourly, monthly, and annually mean clearness index in order to determine the appropriate horizontal diffuse radiation model suitable for tropical climate conditions prevalent in Malaysia. This study revealed that of all models, the Louche and Erbs models were the most accurate in order to estimate diffuse radiation on a horizontal surface. Subsequently, a mathematical method was developed to determine accuracy by using measured data of incident solar radiation on the horizontal and sloped surfaces based on combination of Louche and isotropic models. This model was used to evaluate horizontal global solar radiation components based on estimation of diffuse radiation. The statistical analysis results for 5-stations in Peninsular Malaysia exhibited MBE, RMSE, MBE (%), and RMSE (%) in the ranges of 0.02-0.05, 0.12-0.17, 1.00-2.55, and 5.67-8.27 respectively for averaged diffuse solar radiation based on monthly mean daily and annually mean monthly clearness index. This statistical analysis confirmed the accuracy of the methodology developed in this study.