Solar hydrogen system co-generates heat and oxygen

The solar reactor produces usable heat, oxygen, and hydrogen.

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Synthetic fuels and chemicals from solar energy and abundant reagents offer a possible approach to a sustainable fuel economy and chemical industry.

Researchers from EPFL have constructed a pilot-scale solar reactor that produces hydrogen with a size-unprecedented level of efficiency while also producing useable heat and oxygen.

The EPFL campus has a unique parabolic dish that functions like an artificial tree. A reactor above the dish uses sunlight concentrated approximately 1,000 times to transform water into useful and renewable hydrogen, oxygen, and heat.

Sophia Haussener, 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.”

The team reached the 1-kilowatt limit for the pilot reactor with an output power of nearly 2 kilowatts while maintaining a record-high efficiency for this huge scale. The hydrogen production rate attained in this study is a very positive development for the technology’s eventual commercialization.

A new study builds on preliminary research that demonstrated the notion on a laboratory scale using LRESE’s high-flux solar simulator.

Artificial photosynthesis is the process of producing hydrogen from water using solar energy. However, the LRESE system is unique because it can also produce heat and oxygen at scale.

An integrated photoelectrochemical reactor is located in the focus spot of the dish once the sun’s rays have been concentrated there by the dish.

Photoelectrochemical cells in this reactor electrolyze or divide water molecules into hydrogen and oxygen using solar energy. Additionally, heat is produced, but instead of being wasted as a system loss, this heat passes through a heat exchanger. It is used for various purposes, such as ambient heating.

The oxygen molecules generated by the photo-electrolysis reaction are also collected and utilized in addition to the system’s primary outputs of hydrogen and heat.

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

LRESE-spinoff SoHHytec SA is already using and commercializing the technology, which is appropriate for industrial, commercial, and residential applications.

The EPFL start-up is working with a Swiss metal manufacturing facility to construct a multi-100 kW demonstration plant that will provide heat for the factory’s hot water needs, oxygen for local hospitals, and hydrogen for metal annealing operations.

SoHHytec co-founder and CEO Saurabh Tembhurne said, “With the pilot demonstration at EPFL, we have achieved a major milestone by demonstrating unprecedented efficiency at high output power densities. We are now scaling up a system in an artificial garden-like setup, where each of these ‘artificial trees’ is deployed modularly.”

The system could provide residential power with hydrogen fuel cells, central heating, and hot water for homes and businesses.

The EPFL campus system could meet up to half the electricity demand and more than half the annual heat demand of a typical four-person Swiss household at an output level of about half a kilogram of solar hydrogen per day or power 1.5 hydrogen fuel cell vehicles traveling an average annual distance. With their artificial photosynthesis system, Haussener is already looking into new technical possibilities.

The lab is working on a large-scale solar-powered device that splits carbon dioxide instead of water, producing valuable compounds such as syngas for liquid fuel or the green plastic precursor ethylene.

Journal Reference:

  1. Tembhurne, S., Suter, C., & Haussener,etal. Kilowatt-scale solar hydrogen production system using a concentrated integrated photoelectrochemical device. Nature Energy. DOI: 10.1038/s41560-023-01247-2