Thermo-Radiative Cell - A New Waste Heat Recovery Technology for Space Power Applications

Abstract

In order to satisfy the long-lasting and high energy/power density requirements for NASA deep space exploration missions, Pu-238 has been identified as one of the most suitable radioisotope fuels for GPHS modules since the 1960s. The availability of Pu-238 is currently extremely limited. The limited availability suggests that efficiently using the heat generated by the GPHS is very important and critical for NASA space applications. However, the efficiency of the most widely used radioisotope thermoelectric generators is only about 6-8%, which means that a significant amount of energy is dissipated as waste heat via radiators such as metallic fins. In deep space, the extremely cold universe (3 K) provides a robust heat sink. Even for a heat source with a temperature below 373 K, the corresponding Carnot efficiency can be more than 99%. In this paper, we show a proof-of-concept demonstration of using a thermo-radiative cell, a new technology concept conceived in 2015, to convert heat to electricity. A reversed I-V characteristic between thermo-radiative cell and photovoltaic cell is also experimentally demonstrated for the first time. The predicted efficiency of thermo-radiative cells is significantly higher than thermoelectrics at peak power output, and can be even higher at reduced power output. Integrating thermo-radiative cells with radioisotope heating units (high-grade heat) or radioisotope power system (RPS) radiators (low-grade waste heat) could provide a new way to significantly increase the energy efficiency of Pu-238 or other radioisotope fuels. Preliminary calculations indicate that when combining the thermo-radiative cells with RPS radiators, the thermoelectric RPS efficiency could be increased from 6% to 10-14%, and the dynamics RPS efficiency could be increased from 28% to 34-47%, depending on the radiator temperature.