Theoretical investigation considering manufacturing errors of a high concentrating photovoltaic of Cassegrain design and its experimental validation

Abstract

A compact high concentrating photovoltaic module based on cassegrain optics is presented; consisting of a primary parabolic reflector, secondary inverse parabolic reflector and a third stage homogeniser. The effect of parabolic curvatures, reflector separation distance and the homogeniser’s height and width on the acceptance angle has been investigated for optimization. Simulated optical efficiencies of 84.82 – 81.89 % over a range of ±1 degree tracking error and 55.49% at a tracking error of ±1.5 degrees were obtained. The final singular module measures 169mm in height and 230mm in width (not including structural components such as cover glass).The primary reflector dish has a focal length of 200mm and is afocal with the secondary inverse reflector which has a focal length of 70mm. The transparent homogenising optic has a height of 70mm, an entry aperture of 30 x 30mm and an output aperture of 10 x 10mm to match the solar cell. This study includes an analysis of the optical efficiency, acceptance angle, irradiance distribution and component errors for this type of concentrator. In particular material stability and the surface error of the homogeniser proved to be detrimental in theoretical and experimental testing – reducing the optical efficiency to ~40%. This study proves the importance of material choice and simulating optical surface quality, not simply assuming ideal conditions. In the experimental testing, the acceptance angle followed simulation results as did the optical efficiency of the primary and secondary reflectors. The optical efficiency of the system against increasing solar misalignment angles is given for the theoretical and experimental work carried out.