A spectral beam-splitting architecture is shown to provide an excellent basis for a four junction photovoltaic receiver with a virtually ideal band gap combination. Spectrally selective beam-splitters are used to create a very efficient light trap in form of a 45° parallelepiped. The light trap distributes incident radiation onto the different solar cells with an optical efficiency of more then 90%. Highly efficient solar cells including III-V semiconductors and silicon were fabricated and mounted into the light trapping assembly. An integrated characterization of such a receiver including the measurement of quantum efficiency as well as indoor and outdoor I-V measurements is shown. Moreover, the optical loss mechanisms and the optical efficiency of the spectral beam-splitting approach are discussed. The first experimental setup of the receiver demonstrated an outdoor efficiency of more than 34% under unconcentrated sunlight
The ecological benefit and sustainability of a new energy technology and its potential to reduce CO 2 emissions depend strongly on the amount of energy embodied in the materials and production processes. The energy payback time is a measure for the amount of time that a renewable energy system has to operate until the energy involved in its complete life-cycle is regenerated. In this paper, the energy payback time of the high-concentration photovoltaic system FLATCON 1 using III-V semiconductor multi-junction solar cells has been evaluated. Considering the energy demand for the system manufacturing, including transportation, balance of system and system losses, the energy payback time turns out to be as low as 8-10 months for a FLATCON 1 concentrator built in Germany and operated in Spain. The energy payback time rises slightly to 12 to 16 months for a system installed in Germany. The main energy demand in the production of such a high-concentration photovoltaic system was found to be the zinced steel for the tracking unit.
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