A group of international scientists have written an open letter to UK Prime Minister Boris Johnson to express their concerns that his government's H2 strategy is considering the “widespread use of hydrogen in home heating”.

The experts, led by Cambridge University professor David Cebon, argue that rather than attempting to convert the existing gas grid to use hydrogen — an expensive and difficult proposition ­(see panel below) — the government should instead put its efforts into promoting electric heat pumps “that are more efficient and can already deploy at scale today, supporting thousands of jobs”.

“Hydrogen use in buildings and for road transport is not efficient and does not make economic sense,” they write. “Hydrogen is a not an efficient energy source, which is a fundamental flaw when comparing it with other electrification alternatives.

“Heating buildings with boilers using green hydrogen takes about six times more electricity than using electric heat pumps. That means six times the number of wind turbines or solar panels and a significantly higher cost for consumers.

“Similarly, it takes about 2.6 times more electricity to power a hydrogen fuel cell bus compared to the electricity used for an electric version of the same vehicle.”

Use green H2 only for the things we can’t electrify

The letter argues that developing a green hydrogen industry “is vital — but only for things we can’t electrify”.

“The priority needs to be shifting away from fossil fuels towards efficient electricity-based heating and transport systems, while stimulating the use of green hydrogen for hard to electrify sectors such as steel, chemicals and possibly shipping.”

Grey hydrogen made from unabated fossil fuel should be replaced with the green variety “before considering other end-use sectors or blending [hydrogen into the natural gas grid, which is now being done in a government-sponsored pilot project]”, the scientists say.

As they point out, the production of grey hydrogen­­­ accounts for roughly 3% of the world’s greenhouse gas emissions, about the same proportion as aviation.

“The UK alone produces around 700,000 tonnes of grey hydrogen a year, used to make fertiliser and to remove sulphur from oil. For every kilogram of grey hydrogen produced, the resulting CO₂ emissions are around 9kg, meaning grey hydrogen produces around six million tonnes of CO₂ annually in the UK,” the letter states.

“The case is sometimes made that we need to inject hydrogen into the domestic gas grid to stimulate demand, but this is false: there is already ample opportunity to deploy green hydrogen into facilities currently using grey hydrogen.

“Before considering markets that have existing electrification alternatives, or blending hydrogen into the natural gas grid, grey hydrogen needs to be urgently replaced with zero-emission green hydrogen made from wind and solar energy.”

Blue hydrogen

The seven scientists also call upon the government to “take a cautious approach to blue hydrogen, avoiding lock-in to unsustainable fossil fuel infrastructure that could push net-zero out of reach.”

They write: “By choosing to support blue hydrogen made from natural gas and CCS [carbon capture and storage], the UK must have stringent measures to assess the greenhouse gas emissions from the blue hydrogen manufacturing process and supply chain. Recent research from the US has highlighted the lack of understanding of the climate impacts of blue hydrogen, suggesting that these emissions can be as bad or even worse than simply burning natural gas.

“Assessing the lifecycle emissions of blue hydrogen is a complex issue that will involve auditing and possibly certifying hydrogen production plants, CCS facilities and most of the natural gas supply chain. This could take many years, when electric solutions like heat pumps and EVs are ready to deploy today.”

The letter's signatories are:

  • Professor David Cebon, professor of mechanical engineering, University of Cambridge;
  • Tom Baxter, visiting professor, University of Strathclyde;
  • Dr David Toke, reader in energy politics, University of Aberdeen;
  • Paul Martin, independent chemical engineer, specialising in hydrogen and syngas, Spitfire Research;
  • Bernard van Dijk, lecturer, airplane performance, Univesity of Applied Science, Amsterdam;
  • Professor Neil Hewitt, head of the Belfast School of Architecture and the Built Environment, and director of the Centre for Sustainable Technologies at Ulster University;
  • Jochen Bard, director of energy process technology division, Fraunhofer Institute for Energy Economics and Energy System Technology, Germany.
Converting the gas grid to run on hydrogen

The oil & gas sector argues that hydrogen can be a direct replacement for the natural gas used to heat buildings in many parts of the world, that they could simply pump hydrogen along existing gas networks, with today’s gas-burning appliances swapped out for hydrogen boilers, ovens and stoves.

Yet such a system seems designed to meet the needs of the oil & gas industry, rather than cash-strapped consumers or the climate crisis.

To start with, burning hydrogen results in harmful greenhouse gas emissions — not CO2, but nitrous oxide that form when the flame reacts with oxygen and nitrogen in the air.

Secondly, converting the gas grid to run on hydrogen — which has smaller molecules than natural gas — would require all underground metal gas pipes to be replaced by polyethylene ones — including those concealed in walls and under floorboards in people’s homes. And every gas valve and compressor in the network would also have to be replaced.

On top of this, the energy needed to pump H2 around the gas grid would be three times higher than for natural gas.