The deployment of solar photovoltaic (PV) systems on rooftops in urban environments is to reduce land area required for electricity generation. These deployments may encounter shading and masking on the PV collectors from surrounding building walls, thus reducing the generated electricity. The present article proposes a novel anisotropic diffuse radiation model and investigates the diffuse masking losses stemming from obscuring part of the visible sky to the PV collectors by front rows and by walls erected near the collectors. Monthly and annually collected energies of the anisotropic and the isotropic diffuse radiation models are compared for four different simulated configurations of PV systems deployed near walls. The proposed novel modified model uses the original Klucher (1979) analytical diffuse radiation model for comparing the energies. The anisotropic model predicts a diffuse energy between 4.5% and 13% higher than the isotropic model for a site with 30% diffuse radiation, and nearly 30% higher diffuse energy for a site with 50% diffuse radiation, depending on system configuration. Applying the proposed anisotropic model allows us to assess more accurately the contribution of the diffuse radiation to the generated electric energy of PV systems.
Appelbaum et al. (Sun,) studied this question.