Comparison of the Spherical Optics and Fresnel Lens Performance in a Point-Focus CPV System

The optical system is the component that more affects the performances of a Concentrating Photovoltaic (CPV) system. In this paper, a commonly used Fresnel lens and a less adopted spherical optics of the same diameter, are experimentally compared in a point-focus CPV system from an optical and an energy point of view. The spherical optics allows to reach the optical concentration factor and optical efficiency values equal respectively to 515 and 73%. These values are about three times higher with respect to the Fresnel lens, thus reducing the area of a CPV system with the same power output. Moreover, the spherical optics requires a lower accurate solar tracker with respect to the Fresnel lens, being the acceptance angle values equal respectively to 0.79° and 0.37°. The power and energy losses due to a solar tracking failure are also evaluated for both the optics. The concentration reached by the spherical optics allows also to increase the TJ cell temperature up to 65°C higher than the environmental temperature, and to obtain a cell electrical power equal about to 15 W. As for the Fresnel lens these values are much lower and equal respectively to about 40°C and 5 W. Moreover, the spherical mirror allows the electrical energy production for a longer time in case of a solar tracking failure.