The only way to decarbonise heat generation is by going all-electric, says Barny Evans. And we need to start working on it now.
We are getting closer to an answer to decarbonising our energy system. Electrical generation will almost completely decarbonise, vehicles will electrify, (perhaps even aeroplanes), etc. For heat generation, however, particularly hot water and building heating, there is less consensus and the government is consulting on this to off-gas grid properties now, but the principles apply to on-gas grid properties too.
The government suggests there are three pathways to decarbonising heat generation, but the more you analyse the situation, the more the solution becomes more obvious; electrification is the only realistic way to decarbonise heat at the moment.
‘The CO2 emission factors we use in Building Regulations must be updated now. This will lead to a halving of the CO2 emission factor for electricity and better reflect reality, encouraging all-electric buildings’
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. Though the almost complete decarbonisation of the electrical system produces 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 to meet 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.
Research suggests around 10-20% of the UK’s heat could 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 increases 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 by steam methane reformation (SMR) at around 75% efficiency, with the CO2 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. At present hydrogen is not available in sufficient quantities, nor the appliances or distribution system, so this is not viable in the short/medium term. (Another option, albeit small-scale, is the use of hydrogen created as a by-product of industrial processes.)
But in light of electrification being the only pathway available, I have five suggestions:
- A clear policy that all new build developments should be all-electric. This can be led by government and is easy to achieve: we work on a lot of all-electric 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. New buildings have very low thermal demand.
- The CO2 emission factors we use in Building Regulations must be updated now. DCLG has a methodology for doing this; it is due to be updated in 2019, but this is far too late. By estimation the update will lead to a halving of the CO2 emission factor for electricity and better reflect reality, encouraging all-electric buildings.
- 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.
- 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.
- Develop a plan for electrification. This requires asking Distribution Network Operators, local authorities, developers, companies and asset managers to prepare.
Barny Evans is technical director of energy, waste and sustainable places at WSP