Promises of advanced multi-junction solar cells for the use in CPV systems

III-V multi-junction concentrator solar cells today are optimized for maximum conversion efficiency under AM1.5d standard test conditions at 25 °C cell temperature. But, a higher efficiency for a multi-junction solar cell under these artificial conditions does not necessarily lead to more energy generation in a real photovoltaic concentrator system. The variation of the spectrum during the day and year is crucial to the amount of energy which can be produced. In this paper we calculate the energy which can be harvested on the basis of more than 4000 realistic spectra generated for each daytime hour of the year. Calculations are performed for three typical CPV locations in Colorado, Spain and Israel. A detailed balance approach is used to predict the energy harvesting efficiency for each bandgap combination in a specific multi-junction solar cell. It turns out that all advanced concepts have advantages compared to the state-of-the-art Ga_0.5In_0.5P/Ga_0.99In_0.01As/Ge triple-junction solar cell used today. For example, a monolithic 4-junction device with an ideal combination of bandgap energies could boost the power generation of a CPV system by up to 19 %. Material availability, quality and manufacturing complexity will finally determine the most successful approaches for achieving optimum performance.