Glare potential evaluation of structured PV glass based on gonioreflectometry

Potential glare through reflected sunlight can be a significant hindrance factor for PV installations, especially for building-integrated photovoltaics (BIPV) with atypical orientations and tilt angles present. Structured glass surfaces or antireflective (AR) coatings are often used as a solution, however there currently is no universally recognized method or metric for estimating their impact on glare. This work presents an evaluation of the glare potential of different surface glasses for use in PV modules based on their bi-directional 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 mini-modules are used to characterize the reflectance profiles of eight different glass surfaces. Results for all measured structured glasses, both satinated and macro-textured, show significant reductions in BRDF compared to 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.