Efficiency of a combined solar concentrator cell and thermal power engine system

The combination of a concentrator solar cell and a thermal power engine is investigated theoretically. The excess heat of the PV concentrator cell can be used to drive a thermal power engine such that the thermal engine acts as a cooling device for the solar cell. The combined efficiency of the solar cell and the thermal engine is calculated as a function of cell band-gap energy and temperature. The individual efficiency of the thermal engine was assumed to be one half of that of a Carnot engine. The maximum of the combined efficiency lies between 35 and 40% for concentration factors between 100 and 1000. It can be increased to values above 40% when a tandem configuration for the solar cells is used. By introducing the "double tandem" arrangement, in which the temperature of the cooling medium is raised in stages by first cooling the cell with lowest band-gap and then the higher gap cells, even higher efficiencies of values between 45 and 50% can be achieved theoretically.