Solar power at night? Let’s shed some light on the details
Climate Change Solar Power Renewable Energy

Solar power at night? Let’s shed some light on the details

Dr. Lindy Whitehouse
Dr. Lindy Whitehouse

In 10 seconds? An advancement in thermal capture technology is promising to enable us to harness the sun’s energy at night. A new device developed and tested by researchers in Sydney uses technology that is similar to that found in night vision goggles. But is it efficient?

Wow, that brightened my day… but what’s the breakthrough? Researchers are racing to develop solutions to renewable energy in response to global warming and the need to wean ourselves off fossil fuels. Some scientists have really embraced thinking out of the box and going off the grid by posing the question: what if the energy emitted by the Sun could be harvested… at night?

Tell me why this is not a joke! OK, so it is early days but this is the thinking behind the idea: while solar panels have enabled us to harness solar radiation during the day, there is also a significant amount of energy – originally coming from the Sun - that is reflected back into space from the Earth as infrared radiation. In fact, the Earth continuously emits infrared heat into space at a rate that could power all of humanity several times over! (The average power per square meter measured at an Oklahoma facility in this study was 0.06 kWh/m2. That means, if you take 16.66 m2, you get enough infrared energy to power a ceiling fan for 20 hours or watch 3 hours of programs on a plasma TV.)

It sounds great on paper… Yes, and while previous research has shown that we could theoretically use this energy, a discovery has bought us one step closer to making this a reality. Researchers at UNSW Sydney have developed and tested a device that can capture and convert this infrared heat into electrical power using energy that is otherwise lost to outer space.

Ok, but how exactly does this work? Like solar panels, this new device works on the law of thermodynamics. Solar panels absorb energy from the sun’s light. The greater the temperature difference between the energy-emitting source (the sun) and the absorber (solar panel), the greater the energy produced. This is because at cooler temperatures the electrons found in the silicon in the solar panel cells have less energy when they are cold and so when they are activated by high-energy sunlight, a greater voltage difference occurs which creates more energy, allowing electricity to be produced. In contrast, at night the Earth becomes the warm body and emits infrared light into the cold void of space. The new device aims to capture this infrared light, converting it into energy based on the simple fact: energy can be generated when heat flows from a hotter source to a cooler body.

What happens with infrared radiation hitting the Earth's surface? Part of it contributes to convection and conduction, evaporation, and part of it is emitted into the atmosphere and space. Source: Climate Science Investigations, Florida Atlantic University
What happens with infrared radiation hitting the Earth's surface? Part of it contributes to convection and conduction, evaporation, and part of it is emitted into the atmosphere and space. Source: Climate Science Investigations, Florida Atlantic University

Ok, so how is this new device different from a solar panel? The power-generation device used by the research team is called a thermo-radiative diode and it contains similar technology to that found in night vision goggles! It works by intercepting and harvesting the energy flow directly from the Earth’s surface before it is lost to space. The research team used mid-infrared semiconductor diodes exposed to a cold environment to prove that this energy could be harvested. They also tested the device’s performance across a range of bandgap energies which is the minimum energy needed to excite an electron into a free state so that it can participate in conduction. This information was used to determine the conditions needed for optimal performance and was supported using theoretical models.

Great! So how soon can we expect these devices to be commercially available? OK, while the researchers are radiating with enthusiasm because they proved the concept, there is still quite a way to go before these thermo-radiative diodes become a part of everyday life. The energy produced in these tests was small – approximately just 0.001% of that produced by a solar cell. However, this is the first step in a process that could revolutionize renewable energy, providing new technologies that could enable us to move away from fossil fuels and help keep global warming below 2°C.

Ok, so what’s next? The research team now hopes to attract the attention of industry leaders to help support the development of this new technology and help them refine the devices to make them more efficient. The team will need to identify new materials that could be used to optimize the efficiency of the devices and make them an everyday reality. When that happens, we would be to capture the Sun’s energy 24/7 (in this case the bit that radiates back from Earth). The process could also speed up other research in this area done across the globe. Rune Strandberg, a researcher in Norway, first explored the possibility of capturing infrared radiation from the surroundings and a team at Stanford is also testing ways to capture this energy at night.

Did you know? The idea of capturing solar energy goes back to the 19th Century.

The first steps in creating solar panels occurred in 1839 when 19-year-old Alexandre-Edmond Becquerel, a French experimental physicist, discovered the photovoltaic effect which explained how electricity can be produced from sunlight.

However, it wasn’t until 1954 that researchers at Bell Laboratories created the first practical silicon solar cell that could be used to generate electricity from sunlight.

In 2021, over 10% of the world’s electricity was generated by wind and solar power for the first time! Development of this new technology could see this ratio pushed even higher in the future.

Lindy has distilled 10 research papers saving you 35 hours of reading time.

The Science Integrity Check of this 3-min Science Digest was performed by Dr. ASM Mainul Hasan.

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