Les panneaux solaires absorbent la lumière du Soleil. Inversement, grâce à des « cellules anti-solaires », on pourrait capter la chaleur que le panneau émet vers le ciel nocturne. // Source : Pixabay

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  • What if the solar panels produce energy even at night?

The great limitation of today’s solar panels is that they can only produce energy during the day. The anti-solar cell project would allow them to operate 24 hours a day.

In the face of climate change and its consequences, changing our energy production methods has become an emergency. Several leads have already been developed and have begun to spread. Among them is solar energy. However, there is a problem inherent in this mode of production: it can only work during the day, since the photovoltaic cells in these panels need, by definition, the Sun. At least for now, because a recent invention could revolutionize the very principle of solar panels.

A study published at the end of January 2020, in the magazine ACS Photonics, presents an invention in this sense. These are “solar cells”, i.e. photovoltaic cells that can produce energy even at night. The project is described by its authors as “an alternative photovoltaic concept that uses the Earth as a heat source and the night sky as a heat sink“. Paradoxically, it is through the process of cooling the solar panel that energy could be generated. Explanations.

Les panneaux solaires absorbent la lumière du Soleil. Inversement, grâce à des « cellules anti-solaires », on pourrait capter la chaleur que le panneau émet vers le ciel nocturne. // Source : Pixabay

The solar panels absorb sunlight. Conversely, thanks to “anti-sun cells”, we could capture the heat that the panel emits towards the night sky. // Source: Pixabay

These panels exploit the cold night sky…

Solar panels should be understood as a process of interactivity. A warm object in a colder environment emits its heat in the form of infrared radiation. A cold object will capture and absorb the radiation – and then the heat – that a warmer object sends to it. A traditional solar panel obeys this mechanism. By being colder than the Sun, it will capture its light, therefore its infrared radiation, therefore its heat. Anti-solar cells obey the opposite process.

When night falls, the Sun disappears from the sky and the solar panel points to the Universe – a cold environment. The interaction mechanics are reversed, as the panel becomes the warmest object and emits warm infrared radiation, while the cold night sky absorbs it. The idea of the authors of the project is to integrate into the panel “thermoradiative cells”, the famous “anti-solar cells”: this type of cells can capture the thermal radiation that leaves an object. The idea is that, thanks to these anti-solar cells, the heat that leaves the panel during the night is recovered to produce energy.

“An ordinary solar cell produces energy by absorbing sunlight, which creates a voltage across the device and allows current to flow. In these new devices, the light is emitted in the opposite direction and the current, as well as the electrical voltage, goes in the opposite direction, but you still generate energy,” says engineer and lead author of the project Jeremy Munday in the release.

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How much energy could be produced at night with a solar panel?

At the moment, according to calculations and prototypes related to this project, these inverted solar panels would still not produce as much energy as a conventional solar panel in the middle of the day. But the quantity would not be negligible: 50 watts per square metre under ideal conditions, or 25% of the energy produced during the day. In total, the gain over a full day would be around 12%.

The question that remains to be studied, the authors indicate, is that of the actual construction of this new type of solar panels. “We have to use different materials, but the physics is the same. “And we shouldn’t really call them “solar panels” anymore, but rather “photovoltaic panels”.

That the idea works in principle and that the prototypes are promising is already a good step forward. At present, a solar panel will produce energy during the day, and then at night the system that depends on it must switch to another source – fossil-based. A solar panel capable of operating 24 hours a day would allow us to go further in the energy transition.