Oil & gas firm Repsol by 2024 plans to build a demonstrator plant at its Puertollano industrial complex in Spain for the production of renewable hydrogen by directly tapping solar energy, a process it claims could be commercially viable by the end of the decade.

The Spanish group said it is aiming for the technology – which doesn’t need the intermediate step of electrolysis crucial to other green H2 production methods – to reach "commercial maturity" by 2030. Repsol is developing the process, called photoelectrocatalysis, together with Spanish gas grid operator Enagas.

The demo plant is slated to occupy close to half a hectare and have a production of 100 kilogrammes of renewable H2 per day. It is planned to be followed by 2028 by the installation of an industrial-scale plant of about 60ha and with a production capacity of up to 10 tonnes of the green gas per day.

“It will allow us on the one hand to store renewable energy on a large scale, and on the other to use it as fuel in different sectors such as mobility, in the residential and industrial fields and also as a raw material in industry,” Repsol Technology Lab researcher Ana Martinez said.

While during electrolysis solar or other renewable power is first transported to an electrolyser where the water molecule is separated into H2 and oxygen, photoelectrocatalysis integrates the two steps into a single process.

Scientists have been investigating using sunlight to split water into hydrogen and oxygen.

“The device receives direct solar radiation and using photoactive material generates electrical charges that cause the separation,” said María Dolores Hernández, co-leader of the project.

That avoids losses associated with the transport of electricity, which means that “the photoelectrocatalysis technology improves the efficiency of the process of converting solar energy into hydrogen, with respect to electrolysis.”

Hernández added that the project's roadmap foresees that by 2030 the hydrogen generated directly from solar power will be able to compete in terms of cost with conventional processes using fossil gas, or electrolysis to produce low-carbon hydrogen.

Enagas hydrogen coordinator Monica Sanches added: “It is a very disruptive technology.

“It is part of our commitment to renewable gases, particularly hydrogen and biomethane, as keys to achieving the carbon neutrality that we want to reach at a European level and as a company by 2040.”

Research institutes such as the Catalan Institute for Energy Research, the University of Alicante, and the Aragon Hydrogen Foundation are also involved in the project.

The research has grown from the first concept test of the photoelectrochemical cell of no more than one square centimetre to the start-up in November 2020 of a pilot plant at the Repsol Technology Lab.

Repsol said the renewable hydrogen from the new plant will be applied in refining and chemical processes.

There are other photoelectrocatalysis initiatives in Europe, the US, or Japan, Repsol said.

“But in global terms, we are sure of the great potential of this technology. It will permit the decarbonisation of hydrogen production on an industrial scale, optimising efficiency and costs,” Hernández claimed.

Producing hydrogen directly from solar power without the intermediate step of electrolysis has been the subject of research for years, but so far the technology didn't have a commercial breakthrough yet.

Santa Barbara, California, based company SunHydrogen earlier this year said its partner Suzhou GH New Energy had produced 100 demonstration units that use multi-junction amorphous silicon solar cells to directly produce green H2.

The company with the nano-particle technology intends to provide a proof of concept and demonstrate the potential for scalable growth, and ultimately commercial viability.

SunHydrogen said by optimising the water electrolysis at the nano-level, the company's low-cost nano-particles mimic photosynthesis to efficiently use sunlight to separate hydrogen from water.

UPDATES to add detail on other companies pursuing similar technologies to produce H2 directly from the sun and water.