Glare Potential Evaluation of Structured PV Glass Based on Gonioreflectometry

Abstract

Potential glare through reflected sunlight can be a significant hindrance factor for photovoltaic (PV) installations, especially for building-integrated PVs with atypical orientations and tilt angles present. Structured glass surfaces or antireflective (AR) coatings are often used as a solution, however, there is currently no universally recognized method or metric to estimate their impact on glare. This article presents an evaluation of the glare potential of different surface glasses for use in PV modules based on their bidirectional reflectance distribution functions (BRDF). BRDF threshold values for retinal burn damage, flash blindness, and discomfort glare are calculated based on retinal irradiance thresholds from literature. Subsequently, gonioreflectometric measurements on PV minimodules are used to characterize the reflectance profiles of eight different glass surfaces. Results for all measured structured glasses, both satinated and macrotextured, show significant reductions in BRDF compared with smooth glass, largely eliminating the potential for flash blindness as well as discomfort glare at low incidence angles. At high incidence angles, increased potential for discomfort glare as well as forward scattering along the glass surface can be observed. AR coatings, however, are shown to be insufficient to eliminate glare causing flash blindness.