Description: In response to the NASA STTR solicitation topic T3.01, "Energy Harvesting, Transformation and Multifunctional Power Dissemination", Advanced Cooling Technologies, Inc. (ACT) and Carnegie Mellon University (CMU) propose to develop a thermo-radiative cell to harvest energy from waste heat, for example, from radiators. Currently NASA's Top Technical Challenge is the need to "increase available power". Additionally, NASA has a Grand Challenge as "Affordable and Abundant Power" for NASA mission activities. The thermo-radiative cell technology uses semiconductor p-n junctions, similar to the photovoltaic cell but with smaller band gap semiconductor, to convert heat to electricity. This technology makes use of the extremely cold dark universe (~3K) as the natural heat sink and low-grade waste heat (~50-100℃) as the heat source. The imbalance of the thermal radiation emitted and absorbed by the cell will cause the imbalance of the charge carrier motion in the p-n junction, i.e., generating electrical power. The overall technical objective of Phase I and Phase II projects is to develop a thermo-radiative cell system that can generate practically usable power as supplementary power for the electronics on space vehicles, platforms or habitats. During Phase I, ACT will fabricate a cryogenic system to investigate the performance the thermo-radiative cell made of commercial available InSb, HgCdZnTe, PbSe, or InAs wafers. The cryogenic system will use liquid nitrogen to create a stable low temperature environment. Performance investigation includes the power density and energy efficiency at different heat source temperatures for the non-optimized cell material component and structure in Phase I.

Benefits: The immediate NASA application of this technology is to provide additional power from low grade waste heat, whenever a view of deep space is available. This can be important for outer planet missions. NASA is considering solar power for some NASA outer planet missions, due to the shortage of General Purpose Heat Source (GPHS). Scavenging waste heat to supplement the limited solar power is necessary. In addition, the thermo-radiative cells can improve the efficiency of radioisotope power systems, powered by either thermoelectric or Stirling convertors. Due to the low efficiency of the thermoelectric systems (~7%), there is still significant thermal energy dissipated as low-grade waste heat via the radiator. The proposed thermo-radiative cell technology could satisfy this energy harvesting need and reduce the mass/volume of overall energy systems. In addition, this technology is well-aligned with the NASA Strategic Roadmap (TA 3: Space Power and Energy Storage) as it may have many in-space applications such as on spacecraft or planetary explorers.

Radiative cooling has recently started to commercialize, with companies providing cooling by radiating to the night sky. Additional night time power could be provided by solar power systems, by adding thermal storage and thermoradiative cells to the back of the solar panels. The solar cell side faces up in the daytime. After sunset, the panels can flip to allow the thermo-radiative cell side facing up. Unlike the traditional photovoltaic panel which can only generate electricity in the daytime, this new integrated system can continuously generate electricity for residential use throughout the day and night.