The problems with excessive heat are clear to anyone living in the cities where thermometers posted record highs in summer 2021, and increasingly to lawmakers, who see the health and economic impacts of the raging temperatures
STORAGE POTENTIAL
District heating systems are great ways to store clean energy during times of surplus generation EXPENSIVE TRANSITION
The shift to low-carbon heating networks requires significant investment and more space KEY QUOTE
Perhaps between one third and a half of district heating will come from electricity by 2050 in Europe
Networks for providing heat to homes across whole districts are far from a new idea—some systems were introduced as long ago as the late 19th century, such as in the German city of Hamburg. Though they only make up a small proportion of global heat consumption and remain mostly fuelled by coal or gas followed by bioenergy, many cities have begun to investigate ways to decarbonise them. “District heating shouldn’t be based on one source—it’s just water and pipes, you can heat the water in any number of ways,” says Paul Voss at Euroheat & Power, an industry association. Electricity, solar thermal, geothermal, waste heat and biomass are all low-carbon options and more than one heat source can be combined within the same network, he adds. Heat pumps have been growing in popularity in district heating networks and have a number of advantages, says Ken Brady, programme manager of district heating at the UK’s Energy Savings Trust (EST), which manages the Scottish Government’s District Heating Loan Fund. These include increased efficiency and no impact on air quality, which are particular advantages over biomass systems, he says. They also last longer if maintained correctly—25-40 years as opposed to 10-15 for domestic gas boilers, he adds, making them more attractive to developers considering a whole lifetime cost. Heat pumps can also be grouped in a modular system, which is more resilient than a single gas boiler, he adds. HEAT PUMPS AS STORAGE Voss points to the ability of using large heat pumps as a form of storage by using renewables-generated electricity at times of surplus production to heat water in a DHC network to store it as thermal energy. It is around 100 times cheaper to store energy as hot water, he says. “In this way, thermal and electricity grids can be merged, that’s really positive. In general, I expect electricity to play a much bigger part in district heating networks than they do now—perhaps between one third and a half of district heating will come from electricity by 2050 in Europe,” he says. It may be more like 2030-2035 in the Nordic markets, he adds. BUILDING NEEDS Heat pumps are flexible and can adapt to different building types but are much more suited for use in new build areas because the buildings there typically require lower temperatures to heat. This means that the DHC network can be run at a lower temperature, which in turn lowers the fuel inputs and cost of equipment, Brady says. Heat pumps can also be used in DHC networks serving existing buildings. In these cases, the energy efficiency of the buildings should be upgraded, he stresses. “Building efficiency will affect the design of a system. Where there are very old buildings, there will need to be different types of solutions such as an individual heat pump in a particular building—it can be done, but there’s a cost,” Brady adds. COSTLY RETROFITS Existing heat networks can also be retrofitted to run on heat pumps, according to Jan Rosenow, at advisory body the Regulatory Assistance Project. This could be key in countries in eastern Europe, which are typically run on coal, he says. “There’s a lot of potential but replacing the burning of coal with large-scale heat pumps would mean a very significant investment,” he says. But the costly upgrades should be thought of as a package, not simply the decarbonisation of the fuel supply, he notes. “If you don’t upgrade the efficiency of the buildings or the network and just deal with the fuel source, you’d have to build out a much bigger network which is a lot more costly,” Rosenow says. There might also be a need to upgrade grid infrastructure, says Julien Joubert of Energy Cities, a European advocacy organisation. Amsterdam’s city authority has calculated that its plan to electrify heat will require six hectares of land to install new transformers. “This is an issue for a city that’s already really packed,” Joubert says. Electric boilers can also be used in DHC networks and, though they are less efficient than heat pumps, there could be some cases where they make the most sense, adds Voss. “Electric boilers are cheap and cheerful, so if you only need them for certain situations such as peak times, that only happen a few times a year, it might make more sense to use one over a more expensive heat pump,” he says. City authorities can pull many levers to push the electrification of space heating forward. “Cities have traditionally been fairly passive in terms of energy issues, but in the past five to ten years we’ve seen them play a much bigger role. I think that’s great—they’re typically more ambitious than national counterparts,” Voss says. In order to decarbonise heat, you have to look street by street at what is possible, examine the existing building stock and try to match supply and demand, he says. “You can’t do that without an engaged city,” he says. In some countries, particularly in Germany, the city authority is the owner of the energy company, while in Denmark, the energy company works as a co-op, Voss says. “The more a city is actively engaged in shaping its decisions about energy on its territory, the better it is,” he believes. CITY POWERS While there are some examples of cities that have banned new buildings from connecting to the gas grid, such as California, it is rare for cities to have these kinds of powers, notes RAP’s Rosenow. “It can be hard for cities to make a significant dent in emissions from heating buildings unless they have strong policy support at a national level,” he says. He cites the example of the UK government, which in September launched the £270 million Green Heat Network Fund, a capital grant programme that organisations including city authorities can apply for to gain financial support for heat pumps, solar and geothermal energy to be used in heat networks. PLANNING AHEAD Several city authorities are undertaking area energy planning to identify the potential for heat networks and their sources in a particular area, as well as collect the opinions of potential uses. In Scotland, local authorities have been charged by the central government to undertake energy planning and propose zones for heat networks through new legislation introduced last year. The Scottish Government has also set up a network of free advice centres to provide homeowners impartial advice and support, such as whether they should connect to a heat network and how that would compare with other options. “One thing that city authorities can do to support the roll-out of electrification of heating is to provide consistency of messaging and support for individuals, who could get bamboozled by what some of these things are,” says Anthony Kyrikades at the EST. “It’s hard to find that information in England and Wales and we think that is a gap,” he says. 
LABOUR INTENSIVE In the Netherlands, city authorities already carry out energy planning, along with comprehensive public engagement. This is resource-intensive in terms of staff time, says Energy Cities’ Joubert. A 2020 study commissioned by the Dutch Public Administration Council estimated that a city similar in size and population to Rotterdam would need between 32 and 48 full-time employees to undertake the work required by 2022, doubling by 2030. Cities need support from national governments and the EU to provide this kind of resource, says Joubert. The Netherlands will provide a good testbed for decarbonisation of heat in other cities in Europe, since traditionally around 99% of its heating has come from gas, says Voss. The government has decided to phase out gas heating by 2050. Cities have been mandated to carry out energy planning, which involves going from neighbourhood to neighbourhood working out when various districts can stop using gas, where district heat networks can be installed or where it makes more sense to install heat pumps. Another example of a city innovating in terms of decarbonising district heating is the Finnish capital, which in 2020 launched the Helsinki Energy Challenge to seek ideas to decarbonise its district heating system, having ruled out the use of biomass on sustainability grounds. Finalists were selected from all over the world, with most of the ideas involving electrification technologies such as heat pumps, electric boilers and storage capacity, says Joubert. Despite the fact that Helsinki’s energy company is 100% owned by the municipality, the city still felt that it needed to crowdsource ideas, Joubert notes. “Behind the technical choices, there are political choices, with a lot of criteria to take into account such as efficiency, air quality, land use and impact on resources and jobs,” he says. “The city realised that it needed to step into the debate, to be much more involved in organising the markets and putting people around the table—this is something only cities can do,” he adds.•
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Catherine Early
PHOTO
Mika Korhonen