Night-Time Solar Power: The Future of Satellite Energy

Sunshine is woven into the fabric of life in Australia, but researchers in Sydney are exploring a surprising new way to capture its energy. Instead of just absorbing sunlight, scientists are developing technology that generates power by releasing light, essentially creating a reverse solar panel. This innovation aims to produce electricity even after the sun goes down, tapping into the Earth’s natural nighttime glow.

Jamie Harrison, a postgraduate student at the University of New South Wales, explains the concept. “We’re working on devices that generate electricity by emitting light instead of absorbing it,” he says. He is part of a team at the university’s School of Photovoltaic and Renewable Energy Engineering investigating novel methods for solar power generation. Their focus is on harnessing the infrared radiation, heat energy, that the Earth releases into space at night, a byproduct of the solar energy absorbed during the day.

Professor Ned Ekins-Daukes, who leads the UNSW team, describes the phenomenon. “If you looked at the Earth at night with an infrared camera, you’d see it glowing. The planet is constantly radiating heat out into the cold universe.” The team’s device, a semiconductor called a thermoradiative diode, is designed to convert that infrared radiation into usable electrical current. While not the first group to develop such a diode, the UNSW researchers made a significant breakthrough in 2022 by being the first to directly demonstrate electrical power generation from one.

Currently, the power output is minimal, roughly one hundred-thousandth of what a standard solar panel produces. “It’s enough to power a digital Casio wristwatch from your body heat,” notes Ekins-Daukes. The amount of power generated depends entirely on the temperature difference between the heat source and its surroundings. On Earth, atmospheric gases like water vapor and carbon dioxide trap heat, limiting this differential. Even at peak efficiency, a diode here might only produce about one watt per square meter.

The true potential, according to Ekins-Daukes, lies beyond our atmosphere. In the vacuum of space, the extreme cold provides a perfect environment for the diode to operate efficiently. He envisions this technology providing auxiliary power for satellites, which currently rely on solar panels and batteries. “Particularly in lower orbit, you have 45 minutes of sunlight and then 45 minutes of darkness,” he points out. “The opportunity is to use other surfaces on the spacecraft to generate a bit more power.” The diode would produce electricity from the heat a satellite accumulates in sunlight as it radiates that energy into the frigid void during its dark period.

This could be especially valuable for the growing trend of smaller satellites in low orbits. “The thermoradiative diode could be useful, it is lightweight and generates power from unused surfaces,” Ekins-Daukes adds. The team plans a balloon test flight this year to trial the technology in space-like conditions for the first time.

However, some experts see a different primary application. Dr. Geoffrey Landis, a scientist at NASA’s John Glenn Research Center, notes that for common low-Earth orbit satellites, batteries are a cheap and simple solution. He believes the technology would need to be extremely low-cost to compete. Instead, his research focuses on deep-space missions, such as voyages to the outer planets or rovers in the permanently shadowed craters of the moon.

These missions currently use heavy, expensive thermoelectric generators powered by the decay of radioactive plutonium. Dr. Stephen Polly, who works with Landis at NASA, explains the challenge: “They’re saved for big, flagship missions because plutonium is difficult and expensive to make.” A panel of thermoradiative diodes could offer a more efficient alternative. While still requiring a radioactive heat source, the diode system is simpler, has fewer parts, and could make much better use of the precious plutonium.

A significant hurdle remains: material durability. Current thermoradiative diodes are made from materials similar to those in night-vision goggles and aren’t designed for the intense heat, up to 1000° Celsius, produced by decaying isotopes. “For a space mission, we’d want these semiconductors to last for 10 years, 20 years, maybe even longer,” Landis states. He and Polly are investigating new materials to create a cell that can operate at temperatures up to 375° Celsius. Polly is optimistic, suggesting that if research stays on track, a radioactive isotope-heated thermoradiative system could be feasible within the next decade.

Back at UNSW, Ekins-Daukes’ team has secured funding from the United States Air Force to enhance the diode’s efficiency for use on low-Earth orbit satellites using only solar radiation as a heat source. They are also exploring materials similar to those in conventional solar cells. This approach would allow them to leverage existing manufacturing processes, potentially speeding up commercial production. Ekins-Daukes hopes a practical device could be available within the next five years, opening a new chapter in how we power technology in the darkness of space.

(Source: CNN)