The big limit of current solar panels is that they can only produce energy during the day. The solar cell project would allow them to operate 24 hours a day.
Faced with climate change and its consequences, modifying our energy production methods has become an emergency. Several avenues have already been developed and have begun to spread. Among them is solar energy. A problem is however inherent to this mode of production: it can only work during the day, since the photovoltaic cells of 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 journal ACS Photonics, presents an invention to this effect. These are “anti-solar cells”, that is to say, photovoltaic cells able to produce energy even during the 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 we could generate energy. Explanations.
These panels exploit the cold of the night sky
Solar panels must be understood as a process of interactivity. A hot object in an environment colder than itself emits its heat in the form of infrared radiation. A cold object will capture, absorb, the radiation — and then the heat — sent to it by an object warmer than it. A traditional solar panel obeys this mechanism. By being colder than the Sun, it will capture its light, therefore its infrared radiation, and therefore its heat. The anti-solar cells obey the reverse process.
When night falls, the Sun disappears from the sky and the solar panel then points towards the Universe… a cold environment. The mechanics of interaction reverse, as it is the panel that becomes the hottest object and emits warm infrared radiation, while the cold night sky absorbs it. The idea of the authors of the project is to integrate the panel of “term radiative cells”, the famous “anti-solar cells”: this type of cell can capture the thermal radiation that leaves an object. The idea is that thanks to these anti-solar cells, we recover the heat that leaves the panel during the night, in order to produce energy.
How much energy could we produce at night with a solar panel?
For the moment, according to the calculations and the prototypes, 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 meter 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, say the authors, is that of the actual construction of this new type of solar panels. “We have to use different materials, but the physics are the same. And it shouldn’t be called “solar panels” anymore, but rather “photovoltaic panels”.
That the idea works in principle and that the prototypes are promising is already a good step. Currently, a solar panel will produce energy during the day and then, at night, the installation that depends on it must switch to another source – based on fossil energy. A solar panel capable of operating 24 hours a day would make it possible to go further in the energy transition.
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