Written by Vivian Wang
Illustrated by Anna Tram
As the world’s reliance on fossil fuels continues to threaten our climate, making renewable energy sources accessible is more important than ever. And with over 140 billion USD in investments in 2018 alone, solar power is a key renewable energy source. Using specialised solar cells, we can harness energy from the sun by converting sunlight to electricity. Today, solar panels, which consist of many solar cells, are used to power homes, large-scale commercial projects, and even satellites!
But while they have many advantages, solar panels do have one major limitation: they depend on sunlight so they only work in the daytime! Sure, some panels can store surplus power throughout the night but their batteries are often expensive. To tackle this problem, Jeremy Munday, a professor of electrical and computer engineering at the University of California, Davis, has developed prototypes of solar cells that could potentially generate electricity at night!
So how do these nighttime solar cells work? In his article published in the January 2020 issue of ACS Photonics, Munday proposes a process similar to how normal solar cells work but in reverse, with temperature playing a role. Normal solar cells, also known as photovoltaic cells, are cooler compared to the sun, so they absorb the warmth from sunlight. Conversely, if you point a warm object towards the cold night sky, the object will radiate heat to its surroundings; this is the mechanism that Munday plans to take advantage of with his ‘anti-solar panel,’ which would be made up of thermoradiative cells. At night, these cells would radiate heat towards the cold of deep space which would drive an electrical current through the panel. During the daytime, Munday suggests that the device could continue to generate power if kept away from direct sunlight and the cells could even be heated to enhance electricity production.
Although Munday’s nighttime cells would generate power 24/7, he has to deal with the challenge of making them as productive as normal solar cells. So far, Munday’s prototypes could generate up to 50 watts of power per square meter at night—only about a quarter of what a regular solar panel can produce during daytime.
However, despite the setbacks, Munday’s innovative ‘anti-solar’ cell is a promising step towards producing even better technologies to generate renewable energy. By taking advantage of our planet’s exposure to cold, dark nights, we just might unlock a new path towards around-the-clock sustainable energy!
- Deppe, T., Munday, J. N. (2019). Nighttime Photovoltaic Cells: Electrical Power Generation by Optically Coupling with Deep Space. ACS Photonics, 7(1), 1–9. doi: 10.1021/acsphotonics.9b00679