The Debate around Low-Carbon Heating Systems

Will space heating use hydrogen or electric heat pumps? The solution may not be that simple.

Jon Saltmarsh (Energy Systems Catapult; previously at UK Department for Energy Security and Net Zero) reflects on the polarised debate around how best to decarbonise homes in the UK. Lessons from the UK may have resonance for other nations in their own journey towards low carbon heating in homes.

Like almost everyone involved in this debate I bring considerable past baggage. While working in government I initiated the research and innovation programmes that resulted in the government’s hydrogen for heating trials. I also helped develop the renewable heat incentive that provided financial support to heat pump deployment and the more recent boiler upgrade scheme. I was closely involved with the Energy Systems Catapult’s Smart Systems and Heat programme, a forerunner to Electrification of Heat and I oversaw and published the results from around 50 low carbon heating research and innovation programmes to understand or improve performance. Since moving to the Energy Systems Catapult, I have continued to take a close interest in this vital area of our transition to net zero.

Uncertainty drives inaction

Hardly a day goes by without another article in the press, or comment from a key industry or government figure, on the advantages of either heat pumps or hydrogen as the solution to decarbonising UK homes. Given the definitive and uncompromising way in which many of these arguments are presented, it’s hardly surprising that the reaction of most of the British public is to do precisely nothing. According to European Heat Pump Association figures, the UK has the lowest installation rate of heat pumps per head of population anywhere in Europe (Ambrose 2023).

The reality is that almost anyone replacing a gas boiler today will need to replace it again before hydrogen is even an option. If government takes a decision in 2026 to retain the gas grid for hydrogen distribution, it would then take a minimum of 10 years to plan and build the infrastructure needed to produce and distribute significant quantities of low carbon hydrogen. Only at this point could any structured conversion of areas to hydrogen even begin. The conversion of the UK’s town gas (50% hydrogen) infrastructure to natural gas in the 1960s/70s took over a decade. The conversion of today’s more pervasive gas network will take even longer.

The message from both lobbies should be that decarbonising home heating by switching to electricity is the no regrets option today. There may be alternative solutions in 15 years’ time, but opting for low carbon heating today will have saved upwards of 25 tonnes of carbon emissions from the average home by then. Sadly, by pushing the lines that heat pumps don’t work, and hydrogen is too expensive, people will continue to replace gas boilers with gas boilers.

There are no silver bullets

Elements of the press are often quick to tout the latest silver bullet from a research laboratory that would solve the climate crisis, even people who should know better have referred to hydrogen in this way. The reality is that no single solution will be right to decarbonise all homes. For a start there is always a balance to be struck between energy efficiency and low carbon heating. But even in terms of heating, space constraints, consumer needs, availability of low carbon energy, air quality, aesthetics, location and of course affordability all have a part to play in determining the ‘best’ solution for any particular home.

Energy Systems Catapult’s work on the government’s Electrification of Heat programme has shown that heat pumps can be designed to work in all types of UK homes, from Victorian terraces to 1960s blocks of flats, although space or other constraints might limit their installation in specific cases. Moreover, the Cost Optimal Domestic Electrification study showed that for many types of homes there were two similarly priced solutions; consumers could invest up front in a highly efficient solution, e.g. a heat pump with high capital costs but using less electricity, or they could install cheap inefficient heating, e.g. electric radiators, but spend more on the electricity to power them. The best solution will depend on personal circumstances, the ability to afford upfront costs and what you believe about the direction of future energy prices and interest rates.

Taking a whole system view

What comes across strongly in the debate about the best approach to heating homes has been the lack of a whole system perspective. Simplistic assumptions are made to prove one position or another. The efficiency argument runs that solutions involving hydrogen boilers need 5.5 times more wind turbines than a heat pump solution. As I write this, wind turbines are delivering only 6% of their rated capacity, so if we were to overbuild wind turbines to continue to power heat pumps in these periods of low wind, an equally simplistic analysis would argue for 17 times more wind turbines to be reasonably sure of meeting required demand.

The reality of course is very different. Electricity has to be used at the moment it’s created or converted into another form of energy for storage. Hydrogen is inherently an energy store and therefore can be used many months or indeed years after its creation. Today’s energy system has been built around fossil fuels providing the tens of terawatt hours of storage needed to ensure security of supply. The Royal Society suggests hydrogen is the most cost-effective solution to provide the power and low carbon storage needed to meet this challenge. Where and how this hydrogen is then converted back into electrical energy and heat remains a matter of debate. For example, whole systems modelling, by the Climate Change Committee and by Energy Systems Catapult, demonstrated hybrid solutions, using a mix of heat pumps and hydrogen boilers, can deliver a lower cost solution to meeting peak heat demand than one without hydrogen for heating.

But even whole system models don’t tell the whole story. Firstly, beware spurious accuracy. The level of uncertainty around the cost of a particular decarbonisation pathway is often substantially larger than the difference in cost between alternative pathways. Moreover, by their nature, whole system models make large simplifications to reduce the calculation challenge. Limiting the types of homes modelled reduces complexity immensely. But these simplifications reduce the richness of the results, tending to apply a one size fits all approach. In practice, some buildings, industrial processes or mobility needs might have specific constraints that demand very different solutions.

The UK government has been seeking to reach a clear, evidence-based position on how much of a role hydrogen should play in the future of home heating for the past 5 years. It does not expect to reach a conclusion until the end of 2026. Easy decisions don’t need to be backed up by 8 years of trials and evidence collection.

Financing the transition to net zero

The overall scale of the task to reach net zero is huge. It has already taken decades and we are only just halfway there - the easy half. This commentary has focused on home heating, but the entire power, transport, industrial, commercial, and public sectors all need to be transformed too. This is going to require major upfront investment in manufacturing facilities, infrastructure, and equipment to deliver the necessary changes. There is only so much global investment capital to fund such projects so as other countries accelerate their decarbonisation programmes, we are likely to see a shortage of investment funds, driving up the cost of capital. Pathways that involve lower upfront costs and less need for capital, for example by reusing existing assets rather than paying to decommission them, may well have important short term financial advantages, even if they look less attractive over the long term.

Beware the blank sheet of paper

As noted above, the journey to net zero is a question of transforming what we have today, we can’t start from a blank sheet of paper. Models based around centralised heat generation and storage, feeding heat networks that transport heat to energy efficient homes, typically offer the lowest cost solution when starting from such a position. But the estimated value of the UK housing stock is approaching £9 trillion and that’s a very long way from a blank sheet.

Processes such as PAS 2035 for building fabric retrofit recognise this and provide a set of principles to treat every home individually. But just as there’s no one size fits all for building fabric retrofit, it is necessary to understand the characteristics of a home before identifying the best way to heat it (Eyre et al. 2023). These solutions are also strongly influenced by the local area. Hence, Energy Systems Catapult developed the concept of Local Energy Area Planning, using a structured process to identify the pathway to decarbonisation across a local authority area of interest. Over 70 Local Authorities are now creating or using such plans as a means to understand and meet their declarations of a climate emergency.

Learning from experience

The UK has one of the most pervasive gas networks anywhere in the world and has hence focused closely on whether to repurpose any of it for hydrogen. The UK government embarked on a programme of research and trials to gather the evidence to support this decision. The programme has not progressed entirely smoothly and highlights some useful learning for other gas using nations:

1.     While there is nothing inherently wrong with setting a target date for a decision, to avoid uncertainty and confusion it is even more important to set out clearly the criteria upon which such a decision will be based.

2.     The UK has presented this as a question about hydrogen. But in practice the question is much wider: what is the future of the gas grid? By focusing narrowly on hydrogen, wider issues such as convenience or minimising disruption can get sidelined.

3.     Coupled with this, public engagement needs to focus on moving away from burning natural gas rather than moving to burning hydrogen. This might have removed some of the emotion around hydrogen from the debate.

4.     Finally, there’s a question of scale. Although the UK’s ambition to undertake a village scale (1,000-2,000 homes) trial can be applauded, the reality is small trials are much easier to manage. Smaller, low key hydrogen heating projects driven from within communities in the Netherlands, Germany and Spain have managed to go ahead more quickly and attracted far less opposition.

Conclusions

The present polarised heat pumps versus hydrogen boilers debate is serving only to preserve the status quo although I believe the majority of those involved sincerely believe their position is the right one. It will be very difficult to bring such diverse views together, indeed it may probably futile to try. What is clear is that directing effort to derailing alternative solutions, rather than perfecting your own solution, means that the climate is the big loser.

Even the UK gas industry acknowledges that there are 7 - 10 million homes where there are few limiting factors to installation of a heat pump. Yet the UK Government’s flagship Heat Pump financial support mechanism, the Boiler Upgrade Scheme issued less than 25,000 vouchers for low carbon heating systems in total in 2022. It’s easy to get lost in questions about the best options for each and every home. But the untapped opportunity for all net zero heating technologies completely dwarfs current capability to deliver.

The UK needs to decarbonise more than one home every 30 seconds between now and 2050 to meet our net zero target. This is going to require consolidated effort from the entire heating and insulation industry, all pulling in the same direction, to reshape, retrain and grow the sector to deliver this level of transformational change. By picking the easiest homes to decarbonise today, we can ramp up the capability to deliver, improve installed performance, and drive down costs while continuing to develop technologies that may have a role in 10 years’ time for homes that are more difficult to decarbonise.

References

Ambrose, J. (2023, December 23). Heat pumps are hot property in Europe. Does Britain have cold feet? Guardian. https://www.theguardian.com/environment/2023/dec/23/heat-pumps-are-hot-property-in-europe-does-britain-have-cold-feet

Eyre, N., Fawcett, T., Topouzi, M., Killip, G., Oreszczyn, T., Jenkinson, K., & Rosenow, J. (2023). Fabric first: is it still the right approach? Buildings and Cities, 4(1), pp. 965–972.  https://doi.org/10.5334/bc.388

Rejoinder

The debate continues. See Chris Twinn's essay and response to the above.

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