Calcareous soil rather than very green grass. Sand rather than the surface of a lake. Snow rather than a very brown earth. Which surface is the most judicious to set up a solar power plant ? You know, those rows of photovoltaic panels that we are starting to see blooming from the window of the TGV or near the highways.
Until then, the question arose little. ” At least albedo, that is to say the ability of a soil to reflect sunlight, was not a criterion taken into account in the selection of sites, explains Benoît Posté, innovation project manager at
ENGIE Green, an ENGIE subsidiary specializing in renewable energies. Quite simply because on standard panels, only the front face, directly exposed to the sun, counts. The back side essentially boils down to passing a tangle of threads ”.
The rear face to capture the light reflected from the ground
But that could change with the arrival of bifacial photovoltaic panels. Nothing changes for the front panel. Its mission remains to capture direct sunlight to transform this energy into electricity. But the back side begins to do the same job by capturing the light that is reflected by its environment. The ground mainly. Hence the importance of taking into account your albedo. “The brighter the shade, the better the reflection power., and vice versa, explains Benoît Posté. We thus go from an albedo 0 for a black ground to 1 for a perfect mirror. “
Bifacial technology is not new. “The first patent dates from 1966,” says Benoît Posté. But the technological developments of recent years have meant that the photovoltaic cells that come out today naturally become bifacial and that the price differences are reduced with monofacial panels. “
Are bifacial panels set to become standard technology?
So much so that the bifacial is very quickly becoming the standard technology? This is the opinion of Benoît Posté, which also shares the International Technology Roadmap for Photovoltaics (ITRPV), a roadmap for players in the photovoltaic industry. The 2020 edition predicted that the market share of bifacial photovoltaic modules, still in its infancy today, will increase steadily to reach 45% of new installations in 2024 and 70% in 2030.
What greatly increase the production of electricity from photovoltaics. The innovation project manager at Engie Green tempers: do not expect to do x 2, for example. “The reflected light that gets back from the rear face will remain a significantly lower bearing than that of the front face,” he begins. But we can still hope, in the best case, production gains of up to 10% in bifacial, which means as much in turnover. “
Think differently
As long as you think carefully about how to install these bifacial panels. “We have enough perspective on the monofacial panels to know the configurations and to have taken our habits, continues Benoît Posté. The bifacial will force us to rethink all that. »The albedo will not be the only criterion to be taken into account. “We will also have to play on the height of the tables [sur lesquelles sont apposés les panneaux], knowing that the higher they are, the more light there will be to pass underneath, and the greater the contribution of the rear face will be ”, continues Benoît Posté.
ENGIE Green will thus test, full-scale, four bifacial solar power plants in different configurations. Especially on sites with varied albedos. The first will be put into service in the fall. The others will follow by April 2023. “We are also looking closely at agrivoltaicism,” adds Benoît Posté. The concept ? Install controllable photovoltaic panels above crops to provide shade and protect them from climatic hazards while producing electricity. “For this type of project, priority is given to the needs of the plants, so that the panels are not always turned in the most optimal way towards the Sun,” continues the innovation project manager of ENGIE Green. As a result, electricity production remains lower than for a conventional solar park, which can block certain projects. Here again, bifacial panels could help reduce the gaps. “
This new technology could also offer perspectives on large roofs. Those of factories, logistics warehouses or supermarkets. Even more when they are covered with special paint, like the one used by the Brest-based startup Cool Roof, which reflects up to 95% of the sun’s rays. On the other hand, things get stuck for photovoltaic installations in private homes. “Quite simply because the panels are very often glued to the roof, or even integrated into it,” explains Benoît Posté. Therefore, it has no or very little light to pass below. “
Other valuations of the back side for individuals?
However, even in this configuration, the rear face can participate in the production of energy. In Marseille, the company DualSun has thus developed hybrid photovoltaic panels. “We started from the observation that the popular photovoltaic panels on the home market only produce electricity. And, as such, only use 20% of the solar energy they receive, explains Jérôme Mouterde, who co-founded DualSun with Laëtitia Brottier in 2010. It’s already good and it’s improving, but there is all the same 80% of this energy which is not valorized. And it’s basically a warm-up. “
Therefore, DualSun’s panels are made up of a “classic” front face, with photovoltaic cells that capture direct light to make electricity. “The back side is dotted with small channels. We do there enter water on one side, so that it is distributed in these small channels and comes out heated on the opposite side, ”explains Jérôme Mouterde. This hot water can be used for various uses in the house: helping the boiler to use less gas or fuel oil, heating domestic hot water or swimming pool water. “For the same surface, we produce twice as much energy as a traditional solar panel”, continues Jérôme Mouterde.
DualSun, which has patented its technology and has been marketing its hybrid solar panels for six years, has equipped several thousand buildings – mainly houses – in France and abroad. With the hope of a clear acceleration to come in France, while hybrid solar panels were integrated in 2021 into Ma prime renov, a device to aid energy renovation. The icing on the cake, DualSun, which is one of the twenty start-ups to have joined the new program
French Tech Green 20 of the government, assembles and produces its panels in Jujurieux, in the Ain.
Many other technological advances expected in solar?
The enhancement of the rear face of photovoltaic panels is only one of the technological advances expected to improve the productivity of the solar sector. “Undoubtedly not the most promising even,” indicates Richard Loyen, general delegate ofEnerplan, renewable solar energy union. The perovskites [des cristaux qui promettent d’améliorer grandement la conversion d’énergie solaire en électricité] arrive, the heterojunction solar cells [qui combinent deux technologies différentes en une seule cellule pour pouvoir capter davantage d’énergie solaire] should follow. “
This latest technology alone should allow record yields of 24%, which means that panels equipped with these new cells will be able to recover 24% of the light they receive from the Sun, against 20% on average today. “And we can hope to aim for 30% by 2030,” continues Richard Loyen. In any case, there is continuous technological innovation in solar energy which regularly makes it possible to gain a few percent of additional yields and / or to lower costs. “
But then why is the industry not taking off in France? We only have a little over 10 gigawatts of installed power and solar energy only provides 2.2% of French electricity production. “We should miss the 2023 target set for us by the government [20,6 GW de puissance installée] », Confirms Richard Loyen, who designates as first person in charge the administrative red tape to materialize the projects. “Vietnam installed 13 GW of solar panels last year, when we are at a rate of less than 1 GW per year,” he pleaded.