Effect of Shielding Surfaces on the Irradiance Received by Tilted Collectors

Abstract

A model is developed to predict the total solar irradiance received by a tilted collector in the presence of a large shielding tilted surface. The model is suggested to replace the commonly accepted isotropic model which does not account for a shielding surface. The present model is found to depend mainly on the configuration factors between the collector and the sky and the ground in the presence of a shielding surface. Expressions for these configuration factors are derived for a general geometry of the collector and a large shielding surface. These expressions are found to depend on the tilt angles of the collector and the surface, the orientation angle and the location of the collector relative to the surface, and the height and width of the shielding surface. The expressions are verified numerically and also, by comparing them with the results obtained from the literature for special geometries. The expressions are simplified to facilitate their use for the case of a vertical collector and a vertical shielding surface. This special case is needed to accurately estimate the solar irradiance received by glass windows of buildings.