Generating electricity at night with solar panels? It sounds too good to be true. But according to two American researchers, it is possible. And even with a decent return: under a clear starry sky, up to 25 percent of the daily yield.
Under such ideal conditions, solar panels could provide approximately 50 watts per square meter at night, they state in a journal of the American Chemical Society. It does require thinking. Nighttime residual light is far too weak to generate electricity. The energy therefore does not come from the stars and the moon, but from the earth itself. And not from visible light, but from infrared light (heat radiation).
How does a solar panel actually work? Ordinary solar panels use the sunlight that falls on the top of the panel. This electromagnetic radiation releases electrons in the so-called photovoltaic cells. In an ordinary solar panel, these electrons can only flow in one direction. These electric currents are combined and go as direct current to the inverter of a solar panel. On the other side of that inverter, alternating current comes out, suitable for use or supply to the grid.
Radiation goes from ‘earth panel’ to space
The nocturnal solar panels that researchers at the universities of California and Maryland are developing are working on a similar principle, but the other way around. The radiation goes out from the panel to the outside world. That radiation is the result of the nightly temperature difference between the warm earth’s surface (including the panels) and the cold, dark sky above.
Instead of visible light, infrared light is used: electromagnetic radiation with a lower frequency. Other materials are needed and the direct current flows exactly in the other direction, but further the heat radiation cells that the researchers have in mind function similarly. Since the sun has nothing to do with it, you can actually speak of earth panels. After all, the radiation of the earth is tapped.
There is an important similarity. Because the nightly temperature difference is usually larger in a clear sky, these panels also work best when it is uncloudy. And so the annual return will also be highest in dry (desert) areas.
Source: NU.nl, 26 februari 2020