Solar TE Converter Applications

Abstract

Thermoelectricity does not only serve to profitably recover waste heat from many technical processes but also to exploit renewable energy resources for power generation. Conversion of concentrated solar radiation for decentralized electricity supply is a very promising application field for thermoelectric (TE) devices. However, experimental and theoretical studies with high-temperature resistant thermoelectric oxide modules (TOMs) reveal that 60 % of the incident solar radiation is lost due to reradiation and only 20 % is available for electricity conversion. Calculations with a heat transfer model show that this loss can be substantially reduced from 60 % to only 4 % by using a solar cavity receiver instead of directly irradiated TE modules. The fraction of actually usable solar power can thereby be increased from 20 to 70 %. Despite the improved exploitation of solar radiation, solar-to-electricity efficiency of TOM converters continues to be low due to the still low Figure of Merit ZT of oxide materials. This disadvantage may in part be compensated by higher temperature differences resulting in higher conversion efficiencies. However, due to the temperature dependence of TE properties the use of a single material at a large temperature difference is not ideal. Preferably, a stack of different materials, each operating in its most efficient temperature range, should be applied. Calculations with the heat transfer model show that with a solar cavity-receiver packed with dual-stage cascaded modules containing—in addition to Bi-Te—a TE oxide available at present (ZT=0.36) a solar-to-electricity efficiency of 7.4 % can be achieved. With future advanced oxide materials (ZT=1.7) an efficiency of even 20.8 % seems to be realistic.