Solar reactor turns water into hydrogen

In testing, the new reactor produced about 500 grams of hydrogen per day, meeting about half the electricity needs of a four-person household .

Engineers at the Federal Institute of Technology in Lausanne (EPFL) have successfully built and tested a solar reactor that can produce hydrogen from sunlight and water, New Atlas reported on April 17. The new system is not only highly efficient in producing hydrogen, but also captures byproducts including oxygen and heat for use. The new research was published in the journal Nature Energy.

Parabolic dishes play a key role in a solar reactor that produces hydrogen. (Photo: EPFL)

Hydrogen plays an important role in renewable energy. One of the most efficient ways to produce hydrogen is to split water into its constituent molecules. Doing this using solar energy is called artificial photosynthesis.

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

The reactor captures two byproducts of hydrogen production that are normally wasted: oxygen and heat. The oxygen can be used in hospitals or for industry, while the heat, transferred through a heat exchanger, can be used to boil water or heat buildings.

The team tested the reactor at EPFL's facility over 13 days in August 2020, February and March 2021 to understand how it performed under different weather conditions. The solar-hydrogen conversion efficiency averaged over 20%, producing around 500 grams of hydrogen per day. With this output, the team says, the system could power 1.5 hydrogen fuel cell vehicles (with an average range) for over a year, or cover around half the electricity needs of a four-person household.

'With an output power of more than 2 kW, we have broken the 1 kW ceiling for pilot reactors while maintaining record-high efficiency at this scale. The hydrogen production achieved in the new study represents an encouraging step towards commercializing this technology,' said Sophia Haussener, a member of the research team.

The team plans to build a pilot plant of several hundred kilowatts at a metal manufacturing facility. The hydrogen will be used to anneal metals, the heat will be used to heat water, and the oxygen will be supplied to nearby hospitals.