Interview with Frédéric Vidal, Head of the LUMA platform at INES

Why develop this technology when solar panels linked to water electrolysis are already producing solar-powered hydrogen?

Frédéric Vidal: By definition, research explores new pathways. And when it comes to hydrogen, it's best to have many different ways of producing it. Although we're still at an early stage, Engie has supported us through a project funded by the French National Research Agency (ANR) — a sign that they, the energy sector, are showing serious interest.

In addition, initial laboratory testing has shown conversion efficiencies of 5-10%. Although considerably lower than the efficiencies of standard solar panels in 2025 (20%+), this figure is promising. We also envisage not only panels of several squared meters dedicated to producing hydrogen in this way, but also multifunctional solar panels that produce electricity, generate heat, hydrogen, etc. It's worth looking deeper into both scenarios.

How do photo-electrolysers work?

FV: Let's take the example of the 25 cm² cells produced as part of the EU-funded FreeHydroCells project, in which we are participating. They consist of a plate of glass covered in a transparent conductive film, then transparent photo-electrodes. This entire assembly is dipped in an aqueous solution. The photo-anode, exposed to sunlight, triggers an oxygen gas emission. The photo-cathode, on the other side, uses residual radiation to trigger a hydrogen gas emission.

What challenges have you encountered while developing this technology?

FV: Firstly, the materials used for the electrodes. The titanium dioxide used today has a short lifetime, so we must find alternatives. Then, we must design the entire photo-electrolyser to go around the cell: which optical devices will allow us to make the most of sunlight? How do we manage the distribution and flow of the fluid where the cell is dipped? How do we release the gas bubbles? Especially in the case of hydrogen, which raises safety concerns. What about the temperature and internal pressure? And so on.

What expertise and equipment has Liten contributed to this project?

FV: We are designing a photo-electrolyser prototype using the cells provided by our FreeHydroCells partners. We have provided our expertise in the following areas: mechanics, heat science, fluidics, systems integration, life-cycle analysis... And with Engie, we have carried out techno-economic analyses and reflected on the manufacturing process: the aim is to, one day, produce industrial-scale products.

Are you also responsible for the test bench that will assess the prototypes?

FV: Yes, we have already produced the fluids part and the solar simulator, to internally reproduce the entire spectrum of natural sunlight thanks to PEPR LUMA. Liten has unique expertise in this area. Looking further into the long term, we also envisage external tests in our Inca testing zone, which is dedicated to such testing. But we're taking things one step at a time: for now, we'll finalize our first photo-electrolyzer, with a 25 cm² cell.

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