UC Davis Researchers Propose 'Anti-Solar' Cells to Harvest Energy from Deep Space
New thermoradiative cells could produce electricity at night by radiating Earth's heat into the cold vacuum of space.
Researchers at UC Davis have proposed a new class of "nighttime photovoltaic cells" capable of generating electricity after sunset. The technology reverses the traditional solar process to harvest energy from the temperature difference between the Earth and the cosmos.
Led by Professor Jeremy Munday and graduate student Tristan Deppe, the team detailed the concept in the journal ACS Photonics. Unlike standard solar panels that absorb photons from the sun, these thermoradiative cells generate an electrical current by radiating infrared heat from the relatively warm Earth into the extreme cold of deep space. According to the researchers, the device essentially treats the vacuum of space as a massive heat sink.
The Mechanics of Radiative Cooling
Traditional photovoltaic cells rely on the temperature gradient between the hot sun and the cooler Earth to absorb energy. This new approach flips that dynamic. As Professor Jeremy Munday explained, while a regular solar cell generates power by absorbing sunlight, these devices emit light, causing the current and voltage to flow in the opposite direction while still producing power.
Munday noted that the device operates on the same fundamental principle of utilizing a hot body and a cold body; in this scenario, the Earth serves as the hot body and space as the cold body. To capture the extremely long-wavelength light required for this process, the team is considering the use of mercury alloys for their prototypes.
Potential Impact on Renewable Energy
The theoretical efficiency of these cells is significant. Under ideal conditions, the researchers estimate the cells could generate up to 50 watts of power per square meter at night. This theoretical output is approximately 25% of the power a conventional solar panel produces during the day.
If the technology can be scaled, it would address one of the primary weaknesses of solar energy: intermittency. By providing a continuous source of renewable power throughout the 24-hour cycle, thermoradiative cells could drastically reduce the industry's reliance on expensive, large-scale battery storage systems and help stabilize the power grid.
Future Outlook
While the theoretical framework is established in ACS Photonics, the transition from proposal to commercial application remains the primary hurdle. Future development will focus on the material science required to optimize infrared emission and the practical engineering of cells that can maintain efficiency in diverse atmospheric conditions. For now, the project serves as a proof-of-concept that the cold of deep space can be leveraged as a viable energy resource.