Hydrogen heating heresy

The idea that green hydrogen, produced electrolytically using renewably generated electricity, could be used for home heating has its attractions.  Green hydrogen gas could be piped to homes instead of fossil gas, or, as an interim, admixed with fossil gas to reduce the carbon content. It could be burnt in standard boilers with some marginal adjustment to the jets and make use of the old gas mains, suitably upgraded from iron to plastic, something that is well in hand anyway. So what’s not to like? It’s clean, green, storable and zero carbon and has the virtue of allowing consumers to change energy source without making major changes in their homes. 

Well, that’s now all pretty much a heresy. Hydrogen heating has gone from a ‘good idea’ to a ‘bad thing’ quite quickly. BNEFs Michael Liebreich was one of the first to challenge the over-selling of hydrogen and hydrogen heating in particular. Many others joined in the critique, with the high cost of electrolysis being a major issue and heat pumps being seen as a much better alternative. It’s now got to the point where the US Office of Energy Efficiency and Renewable Energy has posted an apology for inadvertently suggesting earlier that green hydrogen (from off shore wind) could be used for home heating: ‘none of our roadmaps consider home heating a viable use for H2. We expect the more feasible use is decarbonizing heavy industry.’

As that indicates, that doesn’t mean there are not other uses for green hydrogen, but home heating is not now seen as one of them. Instead, electric heat pumps are the big new thing, since their energy conversion efficiency is much higher, with Coefficients of Performance (COP) of 3-4: i.e. you can get three or four times the amount heat out than if you used the electricity directly for heating. The comparison with hydrogen gets even better for heat pumps when you add the 20% or so energy losses incurred by electrolysis to make and use green hydrogen. 

A study in 2021 from University College London concluded that, overall, heat pumps required four times less electricity per unit of heat than green hydrogen, and the heat cost of a green hydrogen-based system was double that of heat pumps. That may have overstated the cost (new electrolysis technology is more efficient and cheaper), but a recent European study has still indicated that heat pumps can deliver heat at around a third of the cost of green hydrogen. 

So is that where the story ends? With, as I noted in an earlier post, the House of Lords environment and climate change committee recently arguing that ‘hydrogen is not a serious option for home heating for the short to medium-term.’ That certainly was the view of a recent US study looking at the proposed use of green hydrogen for heating in Massachusetts. It says that ‘heating buildings is not an appropriate use for green hydrogen’, since it calculated that ‘the supply of electricity needed to produce green hydrogen in quantities necessary to replace the natural gas currently used in buildings in Massachusetts is more than 3.4 times higher than electricity-powered heat pumps’. 

Nevertheless, there are system issues. A switch over from fossil gas to heat pumps will require an expansion of electricity generation. For example in the UK, at present, fossil gas dominates the heating market, with the gas grid supplying around 4 times more energy than is supplied by the power grid overall, with peaks in winter. While heat pumps can sometimes deliver 3-4 times more energy out than with direct use of power (not always- in winter it may be less) that may only compensate for the big expansion of grid power generation needed to run them, and also of the physical power grid.   Of course, if you want instead to supply the heat needed via green hydrogen, although you do have the gas grid, and so do not need to expand the power grid, you will need even more green power generation, since you don’t get the big heat pump gains. The US study gives some figures in that context. It says ‘the total consumption of electricity in Massachusetts for all applications would increase to 2.7 times its current level if all methane in buildings were replaced by100 % hydrogen, whereas the complete replacement of methane combustion systems by heat pumps would increase it to 1.5 times the present level’. 

It also sees some interactive strategic issues in going for hydrogen: ‘Cannibalizing a significant proportion of clean electricity for green hydrogen and diverting it from direct delivery to customers will threaten the imperative goal of achieving grid decarbonization in the power sector, which is critical for plans to reduce emissions in multiple sectors of the economy’. In addition ‘If clean electricity is diverted to the production of green hydrogen, reductions in emissions attributable to electrification in the building sector (e.g. through heat pump installations) will be smaller and slower because such reductions are linked directly to the pace at which grid electricity becomes greener. For the same reason, targets for progressively reducing emissions will remain harder to achieve and potentially out of reach for the transport sector and industrial users despite their investments in electric solutions.’  

So the case against hydrogen for heating does seem quite solid. Green hydrogen will get cheaper as electrolyser technology improves, but not enough to change the situation significantly. Renewable energy costs are falling, so cutting the cost of hydrogen production, but also making it cheaper to run heat pumps. 

There are of course other green options for heating than just heat pumps or hydrogen,  including direct domestic solar heating and large solar heat collector arrays backed up by community scale heat storage. Bioenergy-fired heat networks are also an option. If local heat nets are linked to plants run in biomass-fired Combined Heat & Power (CHP) mode, the overall efficiency can be higher than for heat pumps. With heat storage, CHP plants can also provide flexible balancing for grids. So we need to think in system terms, not just about fitting heat pumps to houses. For example, large heat pumps, can be more efficient than domestic units and can be fed by CHP and linked to large community heat stores to provide flexible power and reliable heat supply. 

Heat pumps do have practical problems. They are relative expensive, and sometimes hard to fit and maintain properly. So it’s not surprising, that consumer take-up can be slow. Moreover, they don’t always achieve high COPs: there can be performance problems in older poorly insulated properties. And in general, heat pumps may not be suited to all homes: for example heat nets may be better in some urban area. There are also issues concerning peak demand. There may be a need for backup for heat pumps to meet winter peaks, possibly via direct electric heating, though there has also been talk of hybrid heat pumps with hydrogen used for backup, though that would mean retaining the gas grid.

So, although their prospects look good in general, there is room for debate about very wide scale heat pump deployment - and certainly they can attract critical commentary. But of course, as we have seen, so can some hydrogen-based systems. And that is not just in relation to green hydrogen for heating.  While green hydrogen may have many other uses (for industrial process heating, some transport and grid balancing), there can be strong environmental objections to any use of blue hydrogen, made from fossil gas with CCS added, and to pink hydrogen, using nuclear electricity. They are seen by most greens as really heretical, whatever their role…