Researchers from the University of New South Wales (UNSW) have developed a means to create electricity from solar radiation at night, potentially resolving the issue of solar renewable energy’s intermittent nature.
The Earth warms up during the day as sunlight hits it, and this heat radiates out into the frigid outer space at night as infrared light. A research team from the University of New South Wales’ School of Photovoltaic and Renewable Energy Engineering has succeeded in generating power from the radiated heat. The scientists employed a thermoradiative diode, which is built from the same components as night vision goggles, to do this.
In a UNSW press statement, Associate Professor Ned Ekins-Daukes, who is leading the research team, said, “We have made an unambiguous demonstration of electrical power from a thermoradiative diode.”
“Using thermal imaging cameras, you can see how much radiation there is at night, but just in the infrared rather than the visible wavelengths,” he said.
“What we have done is make a device that can generate electrical power from the emission of infrared thermal radiation.”
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When hot infrared light is emitted into a colder environment, like the night air, the thermoradiative diode creates electricity by producing a flow of energy across the temperature differential.
“Whenever there is a flow of energy, we can convert it between different forms,” Ekins-Daukes said.
“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,” said Phoebe Pearce, co-author of the article that revealed the discovery.
“In both cases the temperature difference is what lets us generate electricity.”
The thermoradiative process, according to Pearce, is comparable to photovoltaics—the direct conversion of sunlight into electricity—in that it was created by humans to harvest solar power.
“We are diverting energy flowing in the infrared from a warm Earth into the cold universe.”
Presently, the amount of electricity created by a thermoradiative diode is 100,000 times less than the amount of power generated by a solar panel.
“The device works by drawing electrons into the semiconductor as thermal radiation is emitted,” Ekins-Daukes explained in an email.
“Ideally, this is the only process, but unfortunately, in real semiconductor materials, there are other parasitic ways that electrons can find their way to the energy levels responsible for emitting light.
“Our device manages to draw one electron for every 100 photons (particles of light) that are emitted. If we can improve the semiconductor device, we can get closer to a one to one ratio.”
The findings of the UNSW research corroborate a previously undiscovered process, bringing the globe closer to building more efficient and specialized technology to harvest solar energy at night on a far greater scale.
Ekins-Daukes equated the work of the research group to that of Bell Labs engineers, who developed the first solar panel that was efficient enough to be used in 1954. According to the American Physical Society, the Bell Labs solar panel had a conversion efficiency of roughly 6%, but it led to the creation of cells that can translate around 40% of sunlight’s energy into electricity.
The team’s next step, he said, is to design gadgets that would increase the generation of power from infrared light emission.
“At the moment, we are using a photodiode made from a mercury cadmium telluride alloy (HgCdTe) which is used as a sensor in night vision equipment.”
“We will switch to the III-V compound semiconductor system that is easier to work with and allows us more control over the device architecture,” Ekins-Daukes said. “Our device is presently performing at 1/10,000 of its potential, so there is significant scope for improvement.”
The study team believes that the new technology will have a wide range of practical applications, allowing power to be delivered in previously unimaginable ways.
Body heat, which illuminates when observed through a thermal camera, could theoretically be transformed into power using the team’s method, according to Ekins-Daukes.
“Right now, the demonstration we have with the thermoradiative diode is relatively very low power. One of the challenges was actually detecting it.”
“Down the line, this technology could potentially harvest that energy and remove the need for batteries in certain devices–or help to recharge them,” he said. ‘That isn’t something where conventional solar power would necessarily be a viable option.”
Bionic equipment such as artificial hearts, which are now powered by batteries that must be replaced on a regular basis, will benefit from innovation that can remove the need for a battery or produce a rechargeable battery.
“The present diode that we have demonstrated could power a wristwatch from body heat if scaled up to the size of the watch,” Ekins-Daukes said.
He also stated that with minor enhancements, the gadget has the ability to transmit electrical power discreetly at night, “with the evident application for military operations where electronics might need to be powered without a noisy diesel generator.”
“Finally, with a cheap, non-toxic scalable semiconductor material, it would be possible to combine the thermoradiative diode with a solar photovoltaic device, generating electricity from sunlight during the day and thermoradiative power at night,” he said.
The electricity generated at night by infrared light would be roughly 10% of the power produced during the day by sunlight, according to the UNSW researcher, if thermoradiative power is employed in conjunction with the presently used solar panels.
“Even if the commercialisation of these technologies is still a way down the road, being at the very beginning of an evolving idea is such an exciting place to be as a researcher,” Michael Nielsen, co-author of the paper, said.
“By leveraging our knowledge of how to design and optimise 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.”
Industry leaders should recognize the promise of night-time solar technology and promote its development, according to UNSW’s research group.
“I think for this to be breakthrough technology; we shouldn’t underestimate the need for industries to step in and really drive it,” Ekins-Daukes said.
“I’d say there’s still about a decade of university research work to be done here. And then it needs industry to pick it up,” he said. “If industry can see this is a valuable technology for them, then progress can be extremely fast.
“The miracle of solar power today owes itself to world-renowned researchers like Scientia Professor Martin Green at UNSW, but also to industrialists who have raised large sums of money to scale up manufacturing.”
This research expands on the work of a previous group, which includes Andreas Pusch, a co-author of this study, who constructed a mathematical model that this group utilized as a guideline for their tests. The findings of the team’s research have been published in the journal ACS Photonics.