Dual focus Cassegrainian module can achieve ≫45% efficiency

Various types of multijunction solar cells have now been demonstrated with energy conversion efficiencies over 40%. Higher cell efficiencies are still possible. NREL, Fraunhoffer and others have announced ≫40% Inverted metamorphic triple-junction (IMMTJ) InGaP/GaAs/GaInAs cells. One key feature of these cells is that the lowest bandgap cell is no longer a Ge cell. The IMMTJ lowest cell bandgap now allows for a 4th junction cell either integrated or separate. Herein, it is observed that the dual focus Cassegrainian (DFC) module can be fitted with a InGaP/GaAsP/InGaAs triple junction cell at its primary focus and with a GaSb or other IR sensitive cell at its secondary focus. This can allow a straight forward rapid path to a combined cell efficiency of ≫44%. The potential advantages of this configuration are, first, a rapid path to a combined cell efficiency of 44%, and second, given the fact that the heat load is divided into two locations, both cells will run cooler giving a higher module efficiency.