A solar hydrogen system that co-generates heat and oxygen

Newswise —

Despite its unassuming appearance, a parabolic dish on the EPFL campus serves a unique purpose, functioning like an artificial tree. This dish can concentrate solar radiation almost 1,000 times, and a reactor situated above the dish employs this sunlight to transform water into valuable and sustainable products such as hydrogen, oxygen, and heat.

Sophia Haussener, who is the head of the Laboratory of Renewable Energy Science and Engineering (LRESE) in the School of Engineering, said, "This is the first system-level demonstration of solar hydrogen generation. Unlike typical lab-scale demonstrations, it includes all auxiliary devices and components, so it gives us a better idea of the energy efficiency you can expect once you consider the complete system, and not just the device itself."

Dr. Andreas Borgschulte, a researcher in the Laboratory of Renewable Energy Science and Engineering (LRESE), added, “Moreover, our team has shown for the first time that this technology can be effectively scaled up to larger systems, paving the way for commercialization. This is a significant milestone for solar hydrogen generation, which has the potential to play a crucial role in the transition to a low-carbon economy.”

The work builds on preliminary research demonstrating the concept on the laboratory scale, using LRESE’s high-flux solar simulator, which was published in Nature Energy in 2019. Now, the team has published the results of their scaled-up, efficient, and multi-product process under real-world conditions in the same journal.

Waste not, want not

Hydrogen production from water using solar energy is referred to as artificial photosynthesis, but the LRESE system is unique for its ability to also produce heat and oxygen at scale.

The parabolic dish concentrates the sun's rays, which are then focused on an integrated photoelectrochemical reactor where water is pumped. In this reactor, photoelectrochemical cells use solar energy to split water molecules into hydrogen and oxygen. This process also generates heat, which is not lost but instead passed through a heat exchanger, allowing it to be utilized for ambient heating.

In addition to the system’s primary outputs of hydrogen and heat, the oxygen molecules released by the photo-electrolysis reaction are also recovered and used.

“Oxygen is often perceived as a waste product, but in this case, it can also be harnessed – for example for medical applications,” Haussener says.

Industrial and residential energy

The versatility of the system makes it applicable for industrial, commercial, and residential use. The EPFL start-up, SoHHytec SA, is already deploying and commercializing it. The company is partnering with a Swiss-based metal production facility to construct a demonstration plant at the multi-100-kilowatt scale that will produce hydrogen for metal annealing processes, oxygen for nearby hospitals, and heat for the factory's hot-water requirements.

It seems that SoHHytec is taking the technology to the next level by deploying and commercializing it on an industrial scale. The CEO of SoHHytec, Saurabh Tembhurne, mentioned that they are scaling up a system in an artificial garden-like setup where multiple "artificial trees" are deployed in a modular fashion. This indicates that the technology can be easily replicated and scaled up to meet the demands of large-scale hydrogen production for various applications.

That's a promising level of output for the system, and it could have significant applications in both residential and commercial settings. For example, it could provide central heating and hot water, as well as power for hydrogen fuel cells. In terms of specific output, the EPFL system could generate about half a kilogram of solar hydrogen per day, which would be enough to power approximately 1.5 hydrogen fuel cell vehicles driving an average annual distance. Additionally, it could supply more than half of the annual heat demand and up to half of the electricity demand of a typical four-person Swiss household.

That sounds like an exciting avenue of research. Using solar power to split carbon dioxide instead of water could be a game-changer in the development of renewable energy sources and the reduction of greenhouse gas emissions. It's great to see researchers like Haussener and her team exploring new and innovative ways to harness the power of the sun.