Optimization of an ultra-high CPV Cassegrain-Koehler unit with 2000× concentration ratio

In the frame of the Concentrator Photovoltaic (CVP) technology, to achieve ultra-high (UH) concentration levels is a promising strategy to reduce the cost of the PV electricity, since it takes advantage of the reduction of the solar cell area and also of the physical behavior of the solar cells. This work analyzes a previous optical concentrator design for a module with a geometrical concentration of 2000×, i.e. in the range of the UHCPV (ultra-high CPV), in terms of its geometrical design. This optical design can be called Cassegrain-Koehler, since it uses different optical units based on the basic Cassegrain design for telescopes (with a paraboloid primary mirror and with a hyperboloid secondary mirror) as well as takes advantage of the Koehler illumination technique on the solar cell. In order to optimize this design, the f- number of the primary mirrors is varied while the f-number of the secondary mirrors is maintained constant ‒3.5. This allow the impact of the compactness of this UHCPV design to be determined. The results show an optimum trade-off of optical efficiency and acceptance angle when the f-number of the primary mirrors is around 0.63, which is not the most compact design obtained. However, the irradiance uniformity over the solar cell, evaluated through the peak-to-average ratio (PAR) results lowest in the most compact designs.