Blog: Heat decarbonisation in the UK – National scenarios vs practical local options

02 Dec 2020

Emissions from the heat sector

The heat sector in the UK contributed to 37% of total greenhouse gas emissions in 2016. This includes emissions from space heating and cooling, hot water supply, cooking, and supplying heat for industrial processes. The large share of natural gas for supplying heat in domestic buildings is the main source of emissions from the heat sector.

Whilst there has been significant progress in reducing emissions from the electricity generation sector over the last decade, the progress in decarbonising the heat has been very slow. From 2010 to 2018, a 67% reduction in emissions from the electricity generation sector compares with an almost negligible reduction from the residential heat sector.

The decarbonisation of the electricity generation sector has led to a significant drop in the carbon emissions intensity of heat produced by electricity either through heat pumps or resistive heaters. Even with a conservative assumption for heat pump seasonal performance factor (SPF) of 2.5, as of the year 2019, the emissions intensity of heat produced by heat pumps is less than 30% of the emissions intensity of heat produced by a gas boiler. As a result of producing heat by heat pumps, emissions intensity by 2035 could be as low as 16 gCO2eq/kWhth.

Figure 1 – Emission intensity of heat produced by different technologies. Data for the emission intensity of electricity grid was taken from the 2018 BEIS, Updated energy, and emissions projections

National heat decarbonisation scenarios

The scenarios for heat decarbonisation presented in the National Grid, Future Energy Scenario 2020 and The CCC’s analysis of alternative UK heat decarbonisation pathways, 2018 focus on national-level changes and trends. These heat decarbonisation scenarios can be categorised as ‘electrification’, ‘hydrogen’, and ‘hybrid’. In the ‘electrification’ pathway, most of the heat demand is met by electric heating appliances, mainly heat pumps, and resistive heating. In the ‘hydrogen’ pathway, hydrogen boilers are the main technology for heating. In the ‘hybrid’ pathway, heat demand is met mainly by hybrid heat pumps, combining electric heat pumps and hydrogen or biofuel boilers. In a ‘hybrid’ scenario, boilers could run on natural gas blended with biogas or hydrogen to reduce emissions.

Figure 2 summarises the mix of heating technologies prevalent in 2019 and that are considered for proposed 2050 decarbonisation scenarios. A key takeaway message from this figure is that decarbonising the heat sector in the UK requires radical changes in the mix of heating technologies and substantial uptake of low carbon heating technologies. For instance, the number of heat pump installations (including hybrid heat pumps) is expected to reach more than 23 million in 2050 in the ‘electrification’ and the ‘hybrid’ pathways. This requires substantial growth in heat pump supply chain capacity as well as skilled workforce to retrofit heating systems.

Figure 2 – Mix of heating technologies in various decarbonisation scenarios. Data for FES scenarios were taken from [3], and data for CCC scenarios were taken from The National Grid, Future Energy Scenario 2020 (FES: Future Energy Scenario, CCC: Committee on Climate Change, ST: System Transformation, CT: Consumer Transformation, LTW: Leading the Way).

Spatially explicit scenarios for decarbonising heat in domestic buildings

Unlike electricity and gas, the transport of heat over long distances is not feasible considering its technical and economic aspects. Heat needs to be produced locally and therefore the implications of national heat decarbonisation scenarios on local heat supply options must be investigated through detailed consideration of local circumstances. This ensures that whilst heat supply options in local areas align with national strategies, they are practical and maximise exploitation of distributed low carbon heat sources.

Figure 3 – Aligning national strategies with local potentials for heat decarbonisation

Some of the key factors that affect the technical suitability and practicality of using low carbon heating technologies are:

Energy efficiency of buildings and level of insulation

For heat pumps, there is an inverse relationship between the supply temperature and their efficiency. Therefore, to ensure the efficiency of the heat pumps are maximised without compromising the comfort temperature, the buildings should be well insulated. Insulating buildings is often considered to be a pre-requisite for installing heat pumps.

Heat demand density in local areas

The density of heat demand in an area is one of the important factors that determines whether district heating networks are a viable solution for decarbonising the heat supply. For a local area with a known annual heat demand and area (m2), the heat demand density is a helpful criterion to investigate the viability of developing district heating networks.

Legacy energy infrastructure and availability of low carbon heat sources

The availability of existing energy supply infrastructure plays a crucial role in the cost competitiveness of certain heating technologies. For example, buildings that are not connected to gas grid, which potentially could be retrofitted to transport hydrogen, might not be able to use bio-gas or hydrogen for heating. Or the availability of demand headroom in an electricity network substation would avoid the cost of reinforcement when a large number of heat pumps are installed. Furthermore, availability of low carbon and cheap sources of heat such as waste heat from industries would prioritise certain heat supply options.

Availability of space in domestic buildings

When investigating practical heat decarbonisation options for local areas, it is necessary to differentiate between houses with and without space constraints. This helps to identify the number of properties that are unlikely to use technologies that require more space, such as heat pumps or hybrid heat pumps. These systems may require internal space for hot water storage tank and larger low temperature heat emitters. There is a lack of evidence in the area of categorising space-constrained houses and therefore the size of this segment is uncertain. However, a report by Element Energy for the Committee on Climate Change defined a space-constrained home as one with an available dwelling floor area per habitable room of 16 m2 or less. This definition of space availability identifies homes that are most likely to value available space and better represents the available space per occupant. Although this gives an indication of those houses with space constraints, space-constrained houses are likely to be case-specific, depending on dwelling size, layout, number and types of occupants, and customer preference.

The example of Zero2050 South Wales project

As part of the Zero2050 South Wales project, UKERC researchers worked with National Grid to investigate possible pathways for decarbonising heat in cities in South Wales, such that the pathways are aligned with national decarbonisation scenarios whilst considering local circumstances. Detailed analysis of housing stocks, buildings energy efficiency performance, heat demand density, availability of energy supply infrastructure, and space availability in domestic buildings, at Lower layer Super Output Area (LSOA) was carried out to identify technically feasible low carbon heat supply options for Cardiff, Swansea, and Newport which are the three largest cities in South Wales. As an example, Figure 4 presents city-specific scenarios for the decarbonisation of heat in the three cities in South Wales. The share of different low carbon technologies under the same decarbonisation scenario is different for each city due to variations in housing stock and their characteristics in terms of the number of houses located in heat dense areas of the cities, and space availability of buildings. Figure 5 illustrates areas with high heat demand densities that are suitable for developing district heat networks.

Figure 4 – A simplified example of city-specific low carbon heat scenarios. This figure shows percentage of buildings heated by different low carbon heat technologies in an electrification pathway in 2050 (DH: District heating network)

Figure 5 – Areas with high heat density in the cities that are suitable for developing district heating networks

Summary

Decarbonising the domestic heat sector in the UK by 2050 requires a radical uptake of low carbon heating technologies. This highlights the need for strategic planning to prepare the supply chain that includes developing manufacturing capacity and training a skilled workforce.

Further research is required to investigate the implications of national decarbonisation scenarios on local heat supply options. Local circumstances affect the technical feasibility and economic viability of low carbon heating technologies significantly. Furthermore, considering local circumstances in detail allows the quantification of the impacts of various heat decarbonisation pathways on the local energy infrastructure such as reinforcement of low and medium electricity distribution networks.