Generate 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 good return: up to 25 percent of the daily yield under a clear starry sky.
Under such ideal conditions, solar panels could provide a power output of around 50 watts per square meter at night, according to a journal of the American Chemical Society. It does require consideration. Nighttime residual light is far too weak to generate electricity from. The energy 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 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 added together 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.
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Radiation goes from 'earth panel' to space
The nocturnal solar panels for which researchers from the universities of California and Maryland are developing a prototype work on a similar principle, but the other way around. The radiation goes out of the panel. This radiation is the result of the nocturnal temperature difference between the warm earth surface (including the panels) and the cold, dark sky above.
Instead of visible light, it is about infrared light: electromagnetic radiation with a lower frequency. Other materials are needed and the direct current runs exactly in the other direction, but otherwise the heat radiation cells that the researchers have in mind would function similarly. Because the sun has nothing to do with it, it's better to speak of earth panels. After all, the radiance of the earth is tapped.
There is an important agreement. Because the night-time temperature difference is usually greater with a clear sky, these panels also work best when it is clear. And so the annual return will therefore also be highest in dry (desert) areas.
Nocturnal solar panels are actually 'earth panels': they use the nocturnal heat radiation of the earth towards the starry sky. (Image: Tristan Deppe / Jeremy Munday)