Solar Power at Night: A New Twist on Energy

Making Energy from the Sun After Dark

Scientists at the University of New South Wales are pioneering a unique approach to solar energy: generating electricity from the sun's heat even when it's dark. Unlike traditional solar panels that absorb light, their devices emit light to create power—a concept akin to a reverse solar panel.

The Science Behind the Innovation

During the day, the Earth absorbs the sun's heat. At night, this heat is released as infrared radiation, a type of light invisible to the human eye but perceptible as warmth. The team is developing a special semiconductor called a thermoradiative diode, capable of converting this infrared radiation into electricity.

A Breakthrough in 2022

While the concept of a thermoradiative diode is not new, the UNSW team was the first to demonstrate its functionality and electricity production in 2022. Currently, the device generates a minimal amount of power, sufficient to operate a simple digital watch. The power output is influenced by the temperature differential between the heat source and the surrounding environment.

Earth vs. Space: A Comparative Analysis

On Earth, the device's efficiency is limited due to atmospheric gases like water vapor and carbon dioxide, which absorb solar heat and reduce the temperature difference between the Earth's surface and the night sky. In space, however, the absence of an atmosphere creates a much colder environment, significantly enhancing the diode's effectiveness.

Potential Applications in Space

The scientists envision substantial benefits for satellites, which typically rely on solar panels for power. These panels are only operational when exposed to sunlight. In lower orbits, satellites experience alternating periods of sunlight and darkness. The diode could supplement power during the dark phases by converting the satellite's absorbed heat into electricity, which is then radiated into the cold expanse of space.

Advantages for Smaller Satellites

Current satellites use batteries during dark periods, which are charged during sunlight exposure. The diodes offer an additional power source, particularly advantageous for smaller satellites. These satellites operate in lower orbits but perform tasks comparable to larger ones. The lightweight diodes can generate power from surfaces not utilized for other purposes.

Future Testing and NASA's Interest

The UNSW team plans to test the technology in space this year via a balloon flight. Concurrently, NASA is exploring this technology for deep space missions. These missions currently rely on generators that convert heat from radioactive isotopes into electricity. These generators are heavy, expensive, and utilize a rare resource: plutonium.

Enhancing Efficiency and Reducing Resource Dependence

The diodes could optimize the use of plutonium by connecting multiple diodes to form a panel similar to solar cell arrays. The panel would emit waste heat as light, increasing system efficiency and reducing plutonium consumption. However, further research is essential to evaluate the diodes' performance at high temperatures over extended periods. Current thermoelectric systems operate at temperatures ranging from 540° to 1,000° Celsius.

Funding and Future Prospects

The UNSW team has secured funding to enhance the diode for low-Earth satellites. They are also investigating alternative materials akin to those used in conventional solar cells. This could expedite production once the diode becomes commercially available, a milestone the team anticipates within the next five years.