Comparing View Factor modeling frameworks for the estimation of incident solar energy

Abstract

View Factors are instrumental in using widely available horizontal solar radiation data for calculating the incident radiation on harvesting surfaces with arbitrary positions. This capability is notably useful for the design, optimization, and performance forecasting of solar devices. There are several main View Factor models (Liu-Jordan’s, Tian’s, and Badescu’s), which can lead to different theoretical implications and energy estimates. However, the assessments about the validity and underlying assumptions of these models are sometimes contradictory. Resolving this is important for utilizing the most appropriate framework given specific schemes and modeling goals. This work presents a comparative systematic analysis of a wide range of View Factor modeling frameworks with the purpose to gain a deeper understanding of the theoretical consistency and implications of the main View Factor models. The different sets of assumptions are evaluated through stochastic rays simulations and verified against integral models. Five frameworks for the Isotropic and Albedo View Factors were found to be consistent with Liu-Jordan’s model, two with Tian’s, and two with Badescu’s (partially); all with RMSE ⩽0.0014. Considering the most common ways to conceptualize the other components of the radiation, there was consistency with the Perez sky models (RMSE ⩽0.0055) for the View Factor of the Circumsolar radiation as a 25° cone and Horizon Brightening as a flat ring. For the View Factor of the Horizon Brightening as a 6.5° band, two regression models are introduced. By enabling a deeper insight into the sets of assumptions that are consistent with the main View Factor models, this work is valuable for the convergence and best implementation of the various theories in the modeling of incident solar radiation.