Beyond Peak Heat

By Richard Lowes, Energy Policy Group, 30th of April 2019

Around two years ago I released the blog: Is the ‘peak heat’ issue all it’s made out to be? It led to a piece in Utility Week magazine and a response by the Energy Networks Association. My blog discussed the use of the ‘peak heat’ frame by incumbents to imply that gas should be maintained for heating in the UK.  According to the incumbents, if the UK were to electrify much of its heating (as has been shown to be central by much decarbonisation analysis), this would put huge pressure on the electricity system, in the region of hundreds of gigawatts – this, according to incumbents, creates a peak heat requirement which necessitates the continued use of gaseous energy vectors in some form.

My blog of two years ago also explained that there are existing technologies which could significantly reduce that peak demand and which will likely be key components of heat decarbonisation. These include energy efficiency, smart controls and simple thermal storage. The point is, that as heat is decarbonised, it should naturally become less peaky and the peak heat issue becomes less important.

A lot has happened in two years, including:

  • Dramatic cost falls for renewable electricity and electricity storage;
  • Electric vehicles taking off;
  • A cold snap which provided actual data on ‘peak’ gas demand;
  • Social movements around climate change and growing awareness of and interest in low carbon heat technologies.

The ‘peak heat’ argument continues to be pushed (by incumbent interests) as a reason to maintain the gas system while the energy world, and its economics, has changed dramatically. In light of current public interest and the clear need to rapidly decarbonise heating it seems sensible to re-consider this issue and update some of the ideas.

Peak heat update

The excellent analysis by UKERC colleagues last year showed that the peak gas demand on the local gas networks (where nearly all the heat consumption is) was 214 GW on the 1st March at 18:00. With a boiler working at 90% efficiency, let’s call that 193 GW peak heat demand provided by gas[1]. The things I have mentioned already above, better energy efficiency of buildings, more smart controls and greater levels of thermal storage, could have reduced that demand significantly.

But what happens if we electrify that demand? To be clear, it is not as simple as:

xGW of gas demand for heat = xGW of electricity demand

This is because, an electrified heat system wouldn’t rely solely on instantaneous heat demand as the current gas system does and an electrified system can be much more efficient.

A key technology for heat decarbonisation is heat pumps. By extracting heat from the air, ground or water, you end up with more energy provided (or ‘out’ as it is known), than the electricity you put in. Working very well, your ‘coefficient of performance’ (COP) could be four i.e. for each unit of electricity used, four units of heat come out. But let’s be quite pessimistic and use of COP of two.[2]  We’ve just halved the peak heat demand currently provided by gas – it is now 96.5GW.

You now need to forget what you know about how gas boilers work and learn about heat pumps. Gas provides instantaneous high temperature heat. Heat pumps provide lower flow temperatures and are often optimised to run constantly, or for much longer time periods than boilers. Hot water tanks are a requirement too meaning that you can shift hot water load around the day (away from peak times possibly). Research has shown significant potential for load shifting using heat pumps smartly in Germany and Austria. This is a difficult benefit to quantify in the UK (and I’m not sure anyone has[3]), but here is clearly potential to reduce the heat peak further.

And the final piece of the puzzle is the rollout of electric vehicles. There are currently 31 million cars in the UK. A basic Nissan Leaf has a 40kWh battery. If half of the current cars were electric, that’s 620GWh of electrical storage. Of course people won’t want their batteries emptied, but the potential is clear for load shifting and balancing using vehicle to grid technologies. Especially when you consider that the average length of a car journey is 10 miles.

Electrifying much heat and transport, while clearly vital for net zero goals, will required an increase in electricity generation capacity (and probably network capacity too). The key challenge now, is how to integrate renewables, transport and heat in order to reduce spikes in demand and flatten those peaks and make the transformation as (cost) efficient as possible. I argue that we need to move beyond the idea of peak heat and we need to consider overall electricity system flexibility in the context of decarbonised heat and transport.

The key heat question that remains is, how do (or can) the gas networks support this transition? The idea of wholesale conversion of gas networks to 100% hydrogen is unwise, as I have discussed elsewhere. But could the gas networks simply exist to provide a ‘peaking’ service used in conjunction with hybridised heat systems? Perhaps, but then again this could prove to be an expensive and unnecessary insurance option.


N.B. Thank you to Professor Catherine Mitchell and Dr Grant Wilson who’s comments have greatly enhanced this blog. The words however remain the responsibility of the author.



[1] 90% is possibly too high and requires low flow/return temperatures which are not guaranteed; therefore, peak heat demand may be lower. Note that this figure doesn’t include off gas grid heating and does include non-heating local network gas demand.

[2] For reference, some analysis in Ireland showed that even at below negative temperatures, the performance of a number of heat pumps didn’t drop below 3. Higher COPs require lower flow temperatures and therefore more energy efficient buildings can produce higher COPs.

[3] Nicholas Kelly at Strathclyde is one of a few researchers who have considered this at a building level but I am not aware this has been scaled up to a national level.

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