With regard to the decarbonisation of our energy system we are getting closer to an answer; our electrical generation will almost completely decarbonise, vehicles will electrify, (perhaps even aeroplanes), etc. However for heat, particularly hot water and building heating there is less consensus and the government are consulting on this with regard to off gas grid properties now, and the principles apply to on gas grid.

The government suggest there are three pathways to decarbonise heat but the more you analyse the situation, the more the solution becomes more obvious; that electrification is the only realistic way to decarbonise heat at the moment.

The three pathways suggested are:


This would involve replacing boilers, mainly with heat pumps, which use electricity to upgrade heat from the air, ground or water to deliver heat. Though the almost complete decarbonisation of the electrical system gives very low carbon heat, there are still challenges. Heat pumps work best at lower temperatures and therefore energy efficiency is important. The electrical network will require upgrading for increased demand, the public are unused to heat pumps and the supply chain is insufficient to deliver the required retrofitting in the UK at the moment.

District Heating

Research suggests around 10-20% of the UK’s heat could possibly be delivered by district heating. In the past, a benefit of district heating was that it allowed the use of technologies that would not work on individual buildings, such as combined heat and power (CHP) or biomass. Now it is clear gas CHP increase CO2 emissions over a lifetime and biomass heating and CHP have become less favoured due to the air pollution. Instead it is suggested waste heat from “energy from waste” plants, industrial processes and water can be distributed. This will reduce the amount of viable heat networks but improve their CO2 emissions and eliminate air pollution. Here heat pumps are required to upgrade most waste heat and therefore district heating is a sub-set of the electrification pathway.


The mains gas network could be replaced by a hydrogen network, but this would require complete replacement of all appliances and much of the gas network to be upgraded. (Hydrogen could be used to generate electricity in power stations.) Hydrogen must be generated in a way that doesn’t emit CO2 emissions. This can be achieved by electrolysis, at around 30% efficiency or it can be achieved by steam methane reformation (SMR) at around 75% efficiency, with the CO2 being captured and stored. This has never been done at scale and there are questions about how realistic this is in terms of cost and technical issues. As at present hydrogen is not available, nor the appliances or distribution this is not viable in the short/medium term. (Another option, albeit small scale, is the use of hydrogen available as a by-product of industrial processes. )

In light of electrification being the only pathway available now, I suggest 5 things:

  1. A clear policy on all new build developments that they should be all-electric. This can be led by government and is easy, we work on a lot of all-elec. developments. This does not alter existing buildings but it will build the supply chain in terms of products, operation and maintenance, design skills, industry standards, etc. enabling retrofitting of existing properties in future. New buildings have very low thermal demand and so do not place a significant increase in demand.
  2. The CO2 emission factors we use in Building Regulations must be updated now. DCLG have a methodology for doing this. It is due to be updated in 2019 but this is far too late. By estimation when the update occurs it will lead to a halving of the CO2 emission factor for electricity and better reflect reality, encouraging all-electric buildings.
  3. Energy Flexibility must be valued – Consultants cannot account for the fact that the carbon intensity of the electrical system varies a lot depending on the time of day and season. This holds back storage heaters, energy storage, and even heat pumps because the benefit they offer is to use low carbon electricity at periods of low demand, supporting balancing of the grid.
  4. Require retrofit and energy efficiency programmes to prepare buildings to be all-electric. This is likely to include issues  such as ensuring there is space for hot water tanks, a location for an outdoor unit if heat pumps and peak heating demand reduction for storage heaters.
  5. Develop a plan for electrification – This requires asking Distribution Network Operators (DNOs), local authorities, developers, companies and asset managers to prepare for this actively.

This article was written by Barny Evans, Technical Director of Energy, Waste and Sustainable Places at WSP.

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