Thermophotovoltaic Energy Conversion for Space

Abstract

Thermophotovoltaic (TPV) energy conversion cells have made steady and, over the years, considerable progress since first evaluated by Lockheed Martin for direct conversion using nuclear power sources in the mid 1980s. The design trades and evaluations for application to the early defensive missile satellites of the Strategic Defense Initiative found the cell technology to be immature with unacceptably low cell efficiencies comparable to thermoelectric of <10%. Rapid advances in the epitaxial growth technology for ternary compound semiconductors, novel double heterostructure junctions, innovative monolithic integrated cell architecture, and bandpass tandem filter have, in concert, significantly improved cell efficiencies to 25% with the promise of 35% using a solar cell like multijunction approach in the near future. Recent NASA sponsored design and feasibility testing programs have demonstrated the potential for 19% system efficiency for 100 We radioisotopic power sources at an integrated specific power of ∼14 We/kg. The current state of TPV cell technology however limits the operating temperature of the converter cells to <400 K due to radiator mass consideration. This limitation imposes no system mass penalty for the low power application for use with radioisotopes power sources because of the high specific power of the TPV cell converters. However, the application of TPV energy conversion for high power sources has been perceived as having a major impediment above 1 kWe due to the relative low waste heat rejection temperature. We explore this limitation and compare the integrated specific power of TPV converters with current and projected TPV cells with other advanced space power conversion technologies. We find that when the redundancy needed for extended space exploration missions is considered the TPV converters have a much higher range of applicability then previously understood. Furthermore, we believe that with relatively modest modifications of the current epitaxial growth in MOCVD an optimal cell architecture for elevated TPV operation can be found to out-perform the state-of-the-art TPV at an elevated temperature.

Development of a Prototype Thermophotovoltaic Power Generation System Using Super-Adiabatic Combustion in Porous Quartz Glass

“…Much experimental and theoretical work has been conducted on combustion-driven TPV systems to date. (2)(3)(4)(5)(6) However, there has been no combustion TPV systems commercialized as electrical power supplies, because the total conversion efficiency is typically only a few percent. (7) In order to develop a high performance TPV system, the thermal energy of combustion heat must be effectively converted into radiant energy in a usable wavelength band.…”

Ultraefficient thermophotovoltaic power conversion by band-edge spectral filtering

“…We predict that further improvements in reflectivity, series resistance, material quality, and the radiation chamber geometry will push system efficiency to >50%. Such a highly efficient thermophotovoltaic system can have significant impact as a power source for hybrid cars (32), unmanned vehicles (33), deep-space probes (34–36), and energy storage (37, 38), as well as enabling efficient cogeneration systems (39–41) for heat and electricity.…”

Analysis and optimization of In_1-xGaxAsyBb_1-y thermophotovoltaic cells under low radiator temperatures

“…The current TPV cell technology is approaching 30% cell efficiency at 300°k due steady improvement in MOCVD manufacturing process. Through the use of dual junction cells to convert below bandgap photons, further improvements in the cell efficiency are expected to take place over the next few years with expectations of approaching 40% [10].…”