Compatibility approach for the improvement of oxide thermoelectric converters for industrial heat recovery applications

New ceramic Ca3Co3.9O9+δ /CaMn0.97W0.03O3−δ thermoelectric generators with different cross section areas Ap and An of the p- and the n-type leg are fabricated, characterized, and tested at high temperatures in long-term tests. The variation of the measured power output and the efficiency with changing Ap/An ratio is discussed and compared with calculations based on the measured material properties. The highest conversion efficiencies are reached for ratios close to the one predicted by the compatibility approach, whereas an improper choice of Ap/An leads to a strong reduction of the efficiency. A volume power density of 1.4 W/cm3 and an efficiency of 1.08% are found for the most promising generator (temperature difference ΔT= 734 K and Ap/An= 1.12). The results reveal the major importance of the Ap/An ratio for the conversion efficiency and subsequently cost and weight reduction issues, both crucial for a large scale application of thermoelectric converters. Additionally, the oxide generators proved to be very reliable, as after more than 110 h of high temperature energy conversion, no degradation is observable.