The direct conversion of heat energy into electricity is possible by the exploitation of the Seebeck effect in thermoelectric converters (TEC). The commercially available materials for the construction of such converters allow nominal efficiencies up to 5%, quite low compared to other systems using generators coupled to thermodynamic engines. The advantage of a TEC is their reliability because of the absence of moving parts. This type of generating system, heated by isotopic nuclear decay, is used for power supply in spacecrafts designed for long-term planetary exploration missions like Voyager or Pioneer. Comparing the TEC with photovoltaic converters for terrestrial solar energy applications the advantage of the TEC is the possible coupling to a thermal energy storage. The latter combination maybe more cost effective compared to an electric battery storage system. We performed several studies and developments of a TEC coupled to a solar energy receiver. The receiver was designed for the 1 kW DLR dish concentrator DISKUS. A first approach was the construction of a solar TEC based on Bismuth Telluride modules. The receiver temperature has to be limited to 300°C for avoiding a deterioration of the material of the TEC. Furthermore, the receiver design must guarantee a homogeneous temperature distribution over the hot junctions of the TEC. Our tests in a receiver design that was not optimized for low thermal losses gave a direct normal irradiance to electric efficiency of the order of 3.5%. The paper also shows the results of recent tests performed with TEC modules using SiGe semiconducting material. This type of TEC has a high ZT value and best efficiencies in the temperature range of 400-800°C, which is better matched to a solar concentrator like our 1 kW dish. Future plans involve the combination of different module type for increasing the efficiency.
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