EPFL engineers built and tested a solar reactor capable of producing hydrogen from sunlight and water. Not only is the system extremely efficient in producing hydrogen, it also captures “waste” oxygen and heat for use. Hydrogen is poised to become a major player in renewable energy, and one of the most efficient ways to produce it is by breaking down water into its component molecules. When this process is done using solar energy, it’s called artificial photosynthesis, and that’s the process this new reactor uses.

The EPFL reactor looks like a satellite dish and works on a similar principle – a large, curved surface collects as much light as possible and concentrates it on a small device suspended in the middle. In this case, the plate collects heat from the Sun and focuses it about 800 times into a photoelectrochemical reactor. Water is pumped into this reactor, where solar energy is used to split molecules into hydrogen and oxygen.

The reactor also captures the two waste products of the normally newly released process – oxygen and heat. Oxygen can be useful for hospitals or industrial use, while heat passes through a heat exchanger and can be used to heat water or the interior of a building.

The reactor was tested for 13 days at the EPFL campus in August 2020, February and March 2021 to understand how it performs in different weather conditions. Its solar-to-hydrogen efficiency was found to be above 20% on average, producing about 500 g (1.1 lb) of hydrogen per day. At this capacity, the team says, the system could power 1.5 medium-haul hydrogen fuel cell cars for a year, or roughly half the electrical needs of a four-person home.

“With more than 2 kilowatts of output power, we broke the 1 kilowatt limit for our pilot reactor and maintained record high efficiency for this large scale,” said study co-author Sophia Haussener. “The hydrogen production rate achieved in this study is a really encouraging step towards commercial application of this technology.”

The next step, the researchers say, is to build a demonstration facility with a capacity of several hundred kilowatts at a metal fabrication plant, where hydrogen will be used to anneal the metal, heat for hot water, and oxygen collected for nearby hospitals.