Efficiency of concentrator photovoltaic modules based on short-focus Fresnel lenses and A$^3$B$^5$ solar cells

The efficiency of concentrator photovoltaic modules built on the basis of highly efficient cascade GaInP/GaAs/Ge solar cells and 60 $\times$ 60 mm Fresnel lenses of the (“silicon on glass”) type with a shortened focal length has been studied. A simulation of the spatial distributions of photocurrents for subelements of a cascade solar cell was carried out, on the basis of which the current-voltage characteristics and the dependence of the efficiency on the focal length of Fresnel lenses in the range of 85–125 mm. Also the permissible misorientation angle of the photovoltaic module from the direction to the Sun were calculated. It was found that reducing the focal length from 125 mm, which is optimal in terms of efficiency for a lens of the selected size, to 105mm leads to a decrease in efficiency by no more than 0.3 abs.% at misorientation angles up to 2$^\circ$. The consequence of further reduction of the focal length of the lens to 85 mm is a decrease in the efficiency of the module by 0.6-1.2 abs.%.