Debunking Myths: Is Hydrogen the Answer?.
The Government has stated that electric heat pumps, powered by a decarbonised electricity grid, are its ‘preferred mass-market solution’ for zero-carbon home heating in the UK. Accordingly, the next edition of Part L of the Building Regulations, optimistically due to come into force this year, is designed to ensure that natural gas boiler installations are no longer allowed in newbuild homes. However, hydrogen boilers will still be allowed, provided the designed home’s carbon dioxide emissions are lower than those of the same home with a heat pump.
At the time of writing, it’s also a possibility that there will be a ban on all sales of natural gas and oil boilers from 2035, meaning that in 10 years’ time it won’t be possible for householders to buy a replacement for a broken natural gas boiler in an existing home. This ban is due to be confirmed (or otherwise) in the forthcoming Warm Homes Plan.
Arguments in favour of hydrogen
The electric solution for decarbonising our housing has some drawbacks. Switching home heating to heat pumps means that significant electricity grid reinforcement will be required, especially when we are all driving and charging electric cars too. Renewable generation (especially wind and solar) is intermittent, and the generation doesn’t always occur at the same time as we are demanding electricity from the grid; large-scale energy storage will therefore be required as well as thicker (and/or more) wires.
The emissions from hydrogen combustion are essentially benign: just water vapour (with a very small amount of nitrogen oxides). Most current gas boilers can already burn a blend of 20% hydrogen and 80% methane, and pure hydrogen-ready boilers are in development. The Energy Networks Association, which represents the gas and electricity network operators in the UK and Ireland, has stated that our gas grid “is ready for 20% blending”. (That said, it’s important to realise that whilst 20% blend is lower-carbon than natural gas, only pure hydrogen [i.e. 100% blend] is zero-carbon.)
So why don’t we use pure hydrogen in the gas grid?
The ‘colours’ of hydrogen
Natural gas (methane, CH4) is a greenhouse gas, both in itself and because it releases carbon dioxide into the atmosphere when it is burnt. On Earth there are no hydrogen wells like there are natural gas wells, so all hydrogen gas has to be manufactured; whilst hydrogen gas is of course colourless, colours have become a useful shorthand to describe the different ways that hydrogen is manufactured.
The main types of hydrogen available at present are termed grey, blue and green:
- ‘Grey’ hydrogen is manufactured from methane by a thermal process called ‘steam reforming’. When you include the carbon dioxide released from the methane during the reforming, grey hydrogen emits just as much carbon dioxide as burning the methane directly. In fact, once the energy and carbon cost of the reforming process itself is taken into account, grey hydrogen actually emits more carbon dioxide than methane. Nearly all of our current hydrogen is grey (96% according to the Royal Academy of Engineering). Few people would disagree that grey hydrogen cannot be the long-term answer.
- ‘Blue’ hydrogen is grey hydrogen with the carbon that was emitted in its manufacture removed and locked away using a technology known as carbon capture and storage (CCS). Blue hydrogen is arguably a zero-carbon gas, as long as you ignore the energy and carbon cost of the CCS process. However, industrial CCS is not currently operating at scale. Blue hydrogen also locks us into a fossil fuel economy, the emissions associated with gas exploration, extraction, production and transmission remain unmitigated, and many experts believe that its large-scale use will of necessity involve fracking (which amongst other effects releases methane directly to the atmosphere).
- ‘Green’ hydrogen is the least damaging to the environment. It is produced by splitting water (usually seawater) into hydrogen and oxygen using electricity – a process known as electrolysis. As long as the electricity is renewably generated (wind, solar, hydro, nuclear, biomass) there are no carbon dioxide emissions from green hydrogen. The drawback is that it is much more expensive to produce than the other colours, a fact that even environmental organisations such as WWF and Greenpeace do not deny.
So, it seems obvious that for hydrogen heating to be part of a zero-carbon future, the choice of colour is critical – and our starting point is that there is virtually no green hydrogen available, even if we were to accept its high cost.
Further challenges to using hydrogen for home heating
Hydrogen is hard to store, due to its poor compressibility. It is much more explosive than methane at low dilutions. It also has a lower energy content per cubic metre than methane, so will need to be pumped through the gas main at faster flowrates – i.e. higher pressures – which will incur higher pumping energy and will require changes to pressure relief gear.
But most significantly, at more than 20% blending the entire gas main pipework would have to be replaced with different materials (probably polyethylene) and advanced valves. This is because steel becomes brittle and corrodes when in constant contact with hydrogen, and joints and valve seats leak due to the small size of the hydrogen molecule.
Ignoring these challenges, British Gas themselves have stated that even hydrogen blending at 20% will not begin until 2028, and a pure hydrogen gas main will not happen until the 2040s.
Professor David Cebon of the Department of Mechanical Engineering at Cambridge University has stated that “simple thermodynamics tells us that renewable electricity with heat pumps is more efficient – in fact it uses six times less energy – and we do not need more research to tell us so”. He points out that research takes time, needs money, and will delay the urgent rollout of heat pumps when the answer is already clear to us.
The National Infrastructure Commission urged the previous Government in Nov 2023 to reject hydrogen and opt for heat pumps instead. Despite the change in administration, it is understood that Ministers are still “due to decide in 2026”.
So where could or should hydrogen gas be used?
Hydrogen definitely has a part to play in decarbonising some industries, notably processes which use high temperature burners (steel making, glass production, etc.). It is also a necessary component of many chemical feedstocks, for example for fertilisers.
Powering heavy transport is another good application for hydrogen, notably maritime, HGVs, buses, trains and even aviation; this may be via combustion or by using fuel cell based electric motors. Hydrogen could also be a useful storage medium for electricity grid balancing.
Conclusions
Personally, as an independent consultant, a scientist and a great fan of innovation, I’m totally receptive to the arguments in favour of hydrogen. But that said, my strong opinion at present is that we should heat our homes with electricity and heat pumps, and use what hydrogen we can produce for industries and services that cannot be electrified.
In parallel, we should invest heavily in large offshore wind to improve the economics of decarbonising the electricity grid, and in CCS to enable grey hydrogen to be banned. I would also push the Government for some certainty, to stop the hedging and make a clear announcement now rather than in 2026, so we can get on with the strategies that we already know work.
It is also incumbent upon us as consultants and advisors to educate the popular press about the wider issues discussed in this article, to help address the incomplete public understanding of hydrogen. There is much more to it than just “zero emissions at the point of use”.
This article was written by Dr Neil Cutland, Director, Sava