Advanced Cooling Technologies, Inc. (ACT) proposes to develop a novel “dark” photovoltaic cell technology that can generate electricity when there is no sunlight. The proposed “dark” PV technology exploits the thermo-radiative (TR) cell, which is also made of semiconductor p-n junctions and can be viewed as a reversed PV cell, as a new way to efficiently convert heat to electricity when radiatively coupled to a low temperature heat sink. In a previous NASA sponsored program, ACT has successfully demonstrated the proof-of-concept by using commercial narrow-gap semiconductor p-n junctions as thermo-radiative cells to generate electrical power. These results strongly suggested that thermo-radiative cells can be used as a “dark” photovoltaic technology to generate electrical power when the cells face the extremely cold deep space. For example, we could use it to generate electricity during lunar night by utilizing the waste heat from the radiator. We could also use it as an alternative high temperature photovoltaic technology for near-Sun missions that the backside of the cells faces the sun to absorb the solar-thermal energy and the frontside of the cells faces to the dark space. Our modeling results showed that thermo-radiative cells can have a power density up to 1200 W/m^2 when the cell temperature is about 700 K, with an efficiency around 30-40%. To increase the maturity of this technology, ACT, in collaboration with University of Michigan, plans to develop a customized thermo-radiative cell with an area orders of magnitude larger than commercial narrow-gap semiconductor p-n junctions. ACT has a strong R&D team in place to perform the proposed work and a long history of supplying advanced thermal systems for flight applications. The team at UM has a long history working with narrow-gap semiconductor materials, including growth, fabrication and characterization.
The immediate NASA application is to generate electrical power during the lunar night using the waste heat from the radiators of lunar lander. Another potential application is to use TR cell as an alternative technology for high-temperature solar cell, which could be helpful for near-Sun missions (e.g., near Mercury orbit), since the performance of TR cell increases rapidly with temperature. In addition, this technology is well-aligned with NASA Space Power and Energy Storage Roadmap.
Additional night time power can be provided by integrating TR cells to the back of residential solar panels. The solar cell side faces up in the daytime. After sunset, the panels flip to allow the TR cell side face up. Unlike the traditional PV panel which can only generate electricity in the daytime, this new system can generate electricity for residential use throughout the day and night.