Space heating of buildings is a major source of carbon emissions. That need not be the case.

PUMPING UP
The use of electric-powered heat pumps in the UK is minimal, but it is a ready-made alternative to replace individual heating systems common across the country

FINANCIAL BARRIERS
Heat networks are more difficult to introduce in the UK’s busy cities, with banks also reticent to fund these types of projects

KEY QUOTE
Whatever decarbonisation route we take, we need to massively reduce heat demand

The UK has made great strides in sourcing electricity from renewable energy sources, but it is a laggard when it comes to the decarbonising of its heating sector. A bold new vision—featuring district heating, the electrification of heating with heat pumps and investments to increase the energy efficiency of buildings—will not be easy nor cheap to implement, but could allow the UK to make up lost ground. Betting on hydrogen to clean up heating, however, is likely to prove to be a costly distraction if the UK is serious about reaching its 2050 target for net zero emissions. In the UK, 85% of homes are heated by natural gas and the proportion of gas-fired home furnaces, known as boilers in Britain, keeps growing. Some 1.7 million gas boilers were installed in UK households in 2019, up 1.8% from a year earlier, when only 27,000 heat pumps were added. At that rate, the UK Energy Research Centre (UKERC)—a group of academic institutions—says it would take over 700 years to reach the 19 million heat pumps the Committee on Climate Change (CCC), a public body that advises the government on emissions targets, has indicated will be necessary to meet the UK’s binding net zero emission target for 2050.

Heat pumps, which transfer heat from air, water or ground sources using electricity, have the potential to deliver immediate carbon emissions savings of 60-70% compared to conventional electric heating and 55-65% when compared to an efficient gas boiler, figures that can rise when combined with energy efficiency measures to reduce space heating demand, the UK-based non-profit Carbon Trust found in a report released in August 2020 on the opportunities and obstacles to retrofitting existing London homes with heat pumps. As the UK grid continues to decarbonise, heat pumps are seen enabling roughly 90-100% carbon dioxide emissions reduction by 2050, it said.

AN IMMEDIATE FIX

“Heat pumps are now the only readily available net zero carbon solution for heating at scale,” says Will Rivers of Carbon Trust, who stresses that the time to start taking action is now. “We are only 30 years away from 2050 and social housing, for example, invests with a 30-year time horizon.” What makes heat pumps particularly attractive is the prospect that the electricity they use will eventually be from an entirely renewable energy source as the UK power sector shifts from fossil fuels to supply from mainly solar and wind resources, particularly offshore wind.

Heat pumps vary in size from smaller versions for individual buildings to multi-megawatt units for district heating networks in which insulated pipes transport hot water for heating. Heat pumps use less energy to produce the same amount of heat than either gas or electric boilers. The coefficient of performance (COP) for a building heat pump is about three, meaning every unit of energy used to power the heat pump will yield three units of heat energy. Richard Lowes of Exeter University concurs that the “technologically sensible solution” to decarbonising heating in the UK is heat pumps. “We know how to produce low-carbon electricity and there are not many alternatives for heating. There is biomass but there is not so much of that available and there are big questions about its sustainability. There is also solar thermal, but that will not do much for you in the UK in the winter.”

WHAT ABOUT HYDROGEN?

The problem about electrifying heat is that it will be “difficult and costly,” adds Lowes, with major investments needed both for heat pumps and energy efficiency measures. “So we have rapidly seen this idea develop of using hydrogen in the gas grid, which is worrisome because it has never been tried before but has nonetheless risen up the political agenda quickly.”

Not only is it an unproven technology, but hydrogen also looks to be a much more expensive option and could be a greater source of pressure on the electricity grid than the electrification of heating. Heating a house with green hydrogen—which uses renewable energy electricity to power electrolysers that split water into hydrogen and oxygen—would require five times more electricity than doing so with a heat pump, says Jan Rosenow of the Regulatory Assistance Project (RAP), a global think tank on power system strategy. Hydrogen can also be won from a methane source like natural gas, but the required process, “Results in hefty conversion losses and a big problem with carbon capture and storage”, says Lowes. The use of hydrogen for heating is largely being pushed by gas companies. They have, “Seen hydrogen as the best way to keep the gas grid largely as it is while giving politicians a cover to say they have a long-term plan,” says Paul Voss, managing director of Euroheat & Power, an advocacy group. “It would be ridiculously expensive and there are better uses for hydrogen than heating your living room.”

It is possible that stored hydrogen could be used to meet peak heat demand, or be combusted for electricity if a power system reliant on a high share of renewable energy was failing to meet demand, but the prevailing view is that its main role should be reserved for use in hard-to-electrify industrial and transport sectors.

INEFFICIENT BUILDINGS

The CCC has said all new buildings in the UK should be required to have a low-carbon heating solution by 2025 and a natural push towards heat pumps and electrification of heating is expected along with the construction of energy-efficient buildings. But with up to 80% of UK homes built today likely to still be in use in 2050, decarbonisation efforts will fall short unless the inefficiency of older buildings is tackled. “Whatever decarbonisation route we take, we need to massively reduce heat demand,” says Rivers of the Carbon Trust. The UK’s housing stock poses a “considerable threat” to the country’s net zero plans, energy company Engie warned in October 2020 as it unveiled a new low-carbon housing retrofit programme. A study from smart thermostat provider Tado released in February 2020 showed UK homes lost heat up to three times as fast as their European neighbours.

Heat pumps are now the only readily available net zero carbon solution for heating at scale

Research from the UKERC has shown that improving energy efficiency of buildings has potential for cost-effective savings by 2035 equivalent to a 25% reduction in demand. Since some of the housing stock will be more difficult to decarbonise, the Carbon Trust argues that deep retrofits will be necessary in some buildings to make up for others where the possibility of efficiency improvements is limited. Cheap gas means energy efficiency measures are less important from an economic standpoint. Electricity prices in the UK are about triple that of gas but some electricity suppliers offer lower rates for off-peak hours, which consumers with energy efficient houses that retain heat can take advantage of by pre-heating, improving the business case for heat pumps and contributing to the flexibility of the power system, helping to flatten peaks in demand that would otherwise be met by relatively expensive stored energy or a fossil fuel source. The business case for heat pumps could also be bolstered by changing a tax system which favours the consumption of gas over electricity.

The UK government has taken some steps to support building retrofits, such as a €3.3 billion green investment package launched in summer 2020, which includes a €2.2 billion green homes grant to support household energy efficiency measures and heat pumps. Yet Rosenow says government indecision over the use of hydrogen or heat pumps has meant that policy support for the electrification of heating has fallen short. He also highlights the significant practical obstacles to installing heat pumps. “You cannot just take out a gas boiler and in a few hours replace it with a heat pump,” he says. The UK heat pump market is immature, installers are often inexperienced and the upfront costs of a household heating pump are high. “And if you have a really inefficient house, you cannot run the heat pump efficiently,” Rosenow adds.

HEAT NETWORKS

Dave Andrews, an energy consultant, believes district heating should be the UK’s absolute priority, citing the impact a massive shift to individual heat pumps could have on peak winter power loads, the resulting need for investments in grid infrastructure, and difficulties retrofitting old UK homes. “District heating is inherently cheaper than anything else,” says Andrews. He envisions the UK’s expanding fleet of offshore wind farms powering district heating networks that are equipped with megawatt-class heat pumps. Michael King, a district heating expert, notes that the COP of the large heat pumps used in district heating networks is roughly double that of household heat pumps, with one unit of input energy yielding six. Another advantage of district heating is the possibility for large volumes of thermal storage, for example in giant hot water tanks, providing flexibility in the energy system at a small fraction of the cost for battery storage. District heating also allows for flexibility in the heating source, which can evolve over time and can encompass everything from electrification to combined heat-and power plants running on hydrogen, notes Rachel Lee of renewable energy and sustainability consultancy 350 Strategy. She believes they should be the favoured option for cities and built-up areas, although individual heat pumps will be needed in areas where houses are further apart due to heat losses when hot water is transported over longer distances.

District heating currently only represents a niche of the UK’s entire heating market, with estimates in the range of 2-4% of the total. CCC expects about 18% of UK heat will need to come from heat networks by 2050 if the UK is to meet its carbon targets cost effectively. The Greater London government anticipates 25% of the heat and power used by the city will be generated through localised decentralised energy systems by 2025 and considers the development of decentralised heating and cooling networks to be a priority. One innovative example is the Bunhill 2 District Heating facility in Islington, developed by Danish firm Ramboll, which uses waste heat from the London Underground train network alongside heat pumps to provide heating and hot water to 1350 homes. In Glasgow, the Queen’s Quay regeneration housing project in Clydebank features Scotland’s first large water source heat pump project, in which two, 2.65 megawatt heat pumps will extract heat from the River Clyde and feed it into a district heating network providing heating and hot water for the surrounding development. The system also has back-up boilers and a thermal storage system for periods of high demand.

FINANCIAL INCENTIVES

One of the most difficult problems for heat networks can be financing. “A lot of this is about persuading banks that this is not a high-risk investment, that once people are connected to the network they are quite unlikely to disconnect,” says Lee. She suggests one solution for improving the investment framework could be the introduction of incentives, such as the UK’s Contracts-for-Difference system that underpins the market for sales of electricity from renewable energy. Securing upfront demand for heat networks can be facilitated by heat planning, which in turn eases financing, says King. Progress on this front can be seen in Scotland, where every municipality will be required to prepare a 20-year Local Heating and Energy Efficiency Strategy detailing how it intends to meet heat needs. King says district heating is a no-regrets option, but stresses that no matter how the UK chooses to decarbonise its heat, getting off gas will not be easy. “I think that people need to understand that this is going to be hard. You have to decide which is the least difficult route for decarbonisation and will deliver net zero at the lowest cost.” •

TEXT Heather O’Brian PHOTO Gleren Meneghin