Cloud cover-based models for estimation of global solar radiation: A review and case study

Solar radiation data are essential information for designing and studying various engineering systems such as building thermal performance, photovoltaics, solar thermal systems, and passive solar design. Several empirical models have been developed to simulate the available solar radiation on the earth's surface. This article presents a comprehensive review of cloud cover-based solar radiation models (CSRMs) for estimating the hourly global solar radiation (GSR). Many of these models have been developed according to the Angstrom-Prescott relationship for solar radiation and are mainly used to estimate the monthly average daily total solar radiation. Based on the comprehensive review of CSRMs, it could be stated that the Kasten-Czeplak model and the Lam-Li model are comparatively straightforward and precise for estimating the hourly GSR. Furthermore, the study evaluated the selected model (Lam-Li model) to estimate the hourly GSR on the horizontal surfaces for four different cities in Canada. Results revealed that the original Lam-Li model performs within an acceptable range based on the statistical indices (R-2 = 0.77-0.80 and rRMSE = 39.7-44.0%); however, the performance of the newly modified model (M2) from this study performs significantly better (R-2 = 0.8-0.82 and rRMSE = 3.65-39.5%) than the original model (M1).