UNSW researchers have worked out how to harvest energy from light at night. 

A team from the university’s School of Photovoltaic and Renewable Energy Engineering has generated electricity from heat radiated from Earth as infrared light. 

A device called a thermoradiative diode, composed of materials found in night-vision goggles, was used to generate power from infrared light. Although the amount of power generated at this stage is very small – around 100,000 times less than that supplied by a solar panel – the researchers say it is just the beginning. 

The process has been dubbed ‘night-time solar power’ because it is ultimately still harnessing solar power, which hits the Earth during the day in the form of sunlight and warms up the planet.

At night, this same energy radiates back into the vast, cold void of outer space in the form of infrared light with the thermoradiative diode now proven to be able to generate electricity by taking advantage of this process.

“Whenever there is a flow of energy, we can convert it between different forms,” says team lead, Associate Professor Ned Ekins-Daukes.

“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,” Dr Phoebe Pearce, one of the paper’s co-authors, added.

“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. In both cases the temperature difference is what lets us generate electricity.” 

The breakthrough is an exciting confirmation of a previously theoretical process and is the first step in making specialised, and much more efficient, devices that could one day capture the energy at much larger scale.

A/Prof Ekins-Daukes likens the new research to the work of engineers at Bell Labs who demonstrated the first practical silicon solar cell in 1954.

That first silicon solar cell was only around 2 per cent efficient, but now modern-day cells are able to convert around 23 per cent of the sun’s light into electricity.

And Dr Michael Nielsen, co-author of the paper, says: “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”.

“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,” he said. 

The research team believe the new technology could have a range of uses in the future by helping to produce electricity in ways not currently possible.

One of these could be powering bionic devices, such as artificial hearts, which currently run off batteries which need to be regularly replaced.

“In principle it is possible for us to generate power in the way we have demonstrated just from body heat - which you can see glowing if you look through a thermal camera,” A/Prof Ekins-Dauke says. 

“Down the line, this technology could potentially harvest that energy and remove the need for batteries in certain devices - or help to recharge them. That isn’t something where conventional solar power would necessarily be a viable option.”  

More details are accessible here.