Repsol is developing a technology to convert solar energy and water directly into renewable hydrogen, without the intermediate step of electrolysis.
The Spanish oil major is conducting a project into so-called ‘photoelectrocatalysis’ together with Spanish gas provider Enagás and research institutes such as the Catalan Institute for Energy Research, the University of Alicante, and the Aragon Hydrogen Foundation.
"Using this system, we could obtain a renewable hydrogen that is competitive and uses less energy," said Elena Verdú, senior process development scientist at Repsol’s Technology Lab, because its main advantage compared to electrolysis "is that no electricity is used, and it, therefore, does not depend on the electricity price. This results in a significant operational cost reduction.”
Photoelectrocatalysis is at the experimental stage still, but scientists have been investigating using sunlight to split water into hydrogen and oxygen, trying out various materials such as rust to tease the green gas away to mimic photosynthesis.
Producing green hydrogen from renewable energy via electrolysis currently is still much more expensive than its traditional production through natural gas steam reforming.
Low-carbon or zero-carbon hydrogen?
Repsol is both Spain’s leading producer and the main consumer of hydrogen at its industrial complexes. Hydrogen is a key component in refining processes, used in desulfurization and hydrocracking treatments that improve the performance and the environmental quality of refined fuels.
The oil company currently is exploring various production methods to supplant its current use of hydrogen with climate-friendlier methods, as well as to use green hydrogen and ‘low-carbon’ blue hydrogen (produced from gas linked to carbon capture and storage) for the production of synthetic fuels.
“It is estimated that once they are developed in all their potential applications, renewable and low-carbon hydrogen could together make up 10 to 20% of the global energy consumption,” Verdú said.
Repsol hasn’t detailed which shares of the hydrogen it plans to produce will come from low-carbon and how much from zero-carbon technologies, but said it expects hydrogen linked to CCS to become competitive before other alternatives.
“The development of the different applications of low-carbon hydrogen would make it possible for the infrastructures and the market to be more mature and consolidated when renewable hydrogen reaches competitiveness," Verdú claimed, pointing to the still high production costs of green hydrogen made via electrolysis.
In the case of electrolysis production, the most decisive factor is the price of electricity, “which makes up 70-75% of the costs, she said. The expected development of the electrolysis techniques will "reduce the investment and increase their efficiency.”
Next to green and blue hydrogen, and the novel solar-based hydrogen made via photoelectrocatalysis, Repsol said it is also considering to produce renewable hydrogen through the traditional process, but swapping the fossil raw material for material from a biological source, like biomethane.
The biomethane can be obtained from the treatment of biological waste, sewage sludge, domestic organic waste, and industrial or biomass waste. This option makes it possible to continue using the existing plants, the oil firm said.
To ensure that hydrogen-based solutions can become competitive, one of the key conditions will be the development of an appropriate regulatory framework, Repsol stressed. Building on a roadmap approved by the Spanish cabinet in early October, the framework should facilitate novel hydrogen projects and allow them to reach profitability, the company said.
Spain as part of its hydrogen strategy according to the Reuters newswire aims to install 4GW of electrolyser capacity for the production of green hydrogen by 2030.