Reflector materials for two-dimensional low-concentrating photovoltaic systems: the effect of specular versus diffuse reflectance on the module efficiency

Abstract

Photovoltaic modules in two-dimensional low-concentrating systems with specular parabolic reflectors often experience high local irradiance that causes high local currents and cell temperatures. This generally results in power losses. The use of low-angle scattering reflectors gives a smoother irradiance distribution, which results in a higher fill factor. In order to study how the choice of reflector material influences system performance, two different reflector materials (anodised aluminium and lacquered rolled aluminium laminated on a plastic substrate) were compared. The total and diffuse reflectance spectra of the reflector materials were measured, the integrated hemispherical and specular solar reflectance values calculated, and the angular distributions of scattered light investigated. Two geometrically identical 3× concentrating photovoltaic systems with semi-parabolic over edge reflectors of the different materials were tested outdoors. While the anodised aluminium reflector, which had higher hemispherical and specular solar reflectance, resulted in a higher short-circuit current, the low-angle scattering lacquered foil gave a higher fill factor, due to a smoother image of the sun on the module surface, and an equally high calculated annual electricity production. Given its low price, the latter reflector should thus be more cost-effective in low-concentrating photovoltaic systems. Copyright © 2005 John Wiley & Sons, Ltd.