People may no longer need sunshine to harvest solar power. Researchers from University of New South Wales (UNSW) have found a way to generate electricity using the Earth’s radiant infrared heat, creating the opportunity for “nighttime” solar power. The Australian team’s plan goes beyond keeping on the lights in residential homes; they are now taking their new technology to space.
The science behind the discovery

Have you ever seen the world through thermal imaging cameras? With them, you can spot objects that are radiating energy. And like human bodies, the Earth emits heat. During the day, the sun sends energy to our planet, and while some of it is absorbed into the Earth and its atmosphere, the rest is reflected back into space, effectively cooling our planet. This process of absorption and reflection is key for the global energy balance.
Scientists have already discovered how to harness the sun’s energy using solar panels to “gather” the rays and use it to power electronics. However, these researchers have uncovered a way to harness the solar energy the Earth emits after the sun goes down.
Solar energy at night

The UNSW team created a semiconductor device called a thermoradiative diode, using the same materials in night-vision goggles. It successfully generated power from infrared light emissions, according to the study in ACS Publications. At this time, the resulting power is very small compared to what solar panels could capture. However, the researchers believe they will be able to expand the device’s potential.
“We have made an unambiguous demonstration of electrical power from a thermoradiative diode,” said team lead, Associate Professor Ned Ekins-Daukes to the UNSW Newsroom. “Using thermal imaging cameras you can see how much radiation there is at night, but just in the infrared rather than the visible wavelengths. What we have done is make a device that can generate electrical power from the emission of infrared thermal radiation.”
In other words, it harnesses solar power, only it’s on its way back to space instead of onto Earth.
How sunlight becomes power
“Photovoltaics, the direct conversion of sunlight into electricity, is an artificial process that humans have developed in order to convert the solar energy into power. In that sense the thermoradiative process is similar; we are diverting energy flowing in the infrared from a warm Earth into the cold universe,” said one of the paper’s co-authors, Dr. Phoebe Pearce. “In the same way that a solar cell can generate electricity by absorbing sunlight emitted from a very hot sun, the thermoradiative diode generates electricity by emitting infrared light into a colder environment.” She added that the changes in temperature allows electric generation.
The future of solar energy

We may be far from when this technology can be as widespread as solar panels, but the potential is exciting. “By leveraging our knowledge of how to design and optimize solar cells and borrowing materials from the existing mid-infrared photodetector community, we hope for rapid progress towards delivering the dream of solar power at night,” said co-author Dr. Michael Nielsen.
Harnessing power from the human body

The potential doesn’t end at “nighttime” solar energy. The researchers believe this may lead to technology that could harness power from the heat emitted by human bodies. One theoretical example involves people with bionic devices, like artificial hearts. Instead of using batteries that need to be replaced regularly, the device could operate from the natural radiation in the body. Or think of a wristwatch powered by that same heat. Instead of just being able to see body heat through a thermal camera, scientists will be able to harness it before it dissipates into the surrounding air.
Power during an eclipse

As of 2024, the team is working to apply the technology to spacecrafts like satellites. Spacecrafts are powered by solar cells. However, during situations such as eclipses where there is no sunlight, they depend on batteries. So the researchers are working to use their device to generate power in complete darkness.
The thermoradiative diode in space

“The first silicon solar cells were demonstrated in 1953 and by 1958 they were used on the first solar powered satellite,” said Prof. Ekins-Daukes, in an UNSW release in 20204. “We now generate very large quantities of electricity from solar power for our homes using silicon solar cells, that technology which was first used in space. In a similar way, we intend to fly the thermoradiative diode in space within the next two years.”
The success of this endeavor will help fund further development of the technology, namely for it to power day-to-day appliances and homes.
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