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Decarbonised heat within a decade in Denmark

Denmark has led the way on decarbonisation of heating, with a rapid transition away from fossil fuels aided by its large scale adoption of heating networks over the past 40 years. Instead of exchanging individual heating appliances in every home and commercial building, the Danes are centrally converting their heat networks to renewable energy, saving citizens a pile of money in the process

Policies are in place to fully decarbonise Denmark’s heating network

ELECTRIC HEATING
Electricity-based solutions in Denmark are becoming popular as carbon-free renewables generation is increasingly affordable

DATA SOURCING
Largely untapped, research is underway in using the heat from data centres in district networks

KEY QUOTE
Heat is easier and cheaper to store than power

Denmark has a head start in eliminating fossil fuels from its heating, with two- thirds of households served by district heating networks, which cover over half the country’s entire heating needs and source about 60% of their heat from carbon-neutral energy sources. Coal and natural-gas fired combined heat-and- power (CHP) is on its way out along with individual oil and gas furnaces in homes. On their way in are biomass CHP, with the emphasis on heat, and heat pumps. The Danish energy and utilities sector is targeting an over 95% reduction in emissions compared to 1990 levels by 2030, with heating to be a major contributor in achieving that goal. Denmark’s overall aim for the same time span is a 70% reduction in emissions. The phasing out of coal in CHP should lead to a reduction of six million tonnes of carbon emissions, while replacing oil and gas in individual heating systems and natural gas and oil in district heating is set to cut emissions by a further four million and one million tonnes, respectively, according to a roadmap from the Danish government’s climate partnership” with the energy and utilities sector. By 2030, the continuing transition to renewables and further energy efficiency improvements should reduce emissions from the energy sector to one million tonnes annually, from 32 million tonnes in 1990, representing half all Denmark’s projected cuts.

Many utilities already replaced coal in CHP plants with biomass,” says Steen Schelle Jensen, a heating and cooling specialist at Kamstrup, a provider of energy solutions. The next step is electrification and sector coupling.” Decarbonisation is made easier by the country’s extensive district heating network. It is an advantage because if you want to change something you only need to do it one place instead of in every single house,” points out Per Alex Sørensen of sustainable energy consultancy PlanEnergi. While the increased use of heat pumps in district heating, individual heating systems, and industry will contribute to a reduction in anticipated overall Danish energy use in 2030, the sector roadmap also sees them boosting demand for electricity by about nine terawatt hours (TWh) in the same period. Heat pumps run on electricity to transfer heat from air, water or the ground to an indoor space. but use far less energy to produce the same amount of heat as traditional heating appliances.

ELECTRIC BOILERS AND HEAT PUMPS

Birger Lauersen of the Danish District Heating Association says its members are increasingly investing in electricity, both with electric boilers that are quite cheap and relatively easy” to put into place and heat pumps, which are more efficient but a bit trickier” and require access to a heat source whether from the ambient heat in air outdoors, from seawater, or low-temperature industrial waste heat, none of which could be efficiently exploited in the days before heat pumps. The big heat pumps used in district heating are largely bespoke solutions, Lauersen says, and adopt different solutions to the site-specific technical challenges of upgrading heat to a temperature at which it can be used in a network.

Lauersen says the decarbonisation of heat in Denmark will lead to the expansion of district heating to some of the 375,000 households still using gas and 75,000 households using oil boilers. Denmark has about 2.7 million households. District heating is a large-scale solution with benefits of scale, including flexibility, but it is not feasible everywhere. Individual heat pumps are more suitable in areas with low heat density,” he says.

One element of flexibility in district heating is that it allows for the use of multiple heat sources—including solar thermal, geothermal, biomass and industrial waste heat—while household heat pumps are bound to electricity. For district heating, the first priority is to use direct heat from a renewable resource, but when supply of renewables-generated electricity exceeds grid demand for it, meaning prices are low, it can make sense to use electricity directly, says Jensen. That flexibility can also help to facilitate power system operation, where supply and demand for electricity must always be in balance. When Danish wind turbines are turning in the middle of the night and demand and prices dip, their output can be channelled to heating water stored in the district heating system. Heat is easier and cheaper to store than power.

Forfatterhuset kindergarten by COBE architects. District heating keeps the kids at this Kindergarden warm. Photo by Rasmus Hjortshøj, COAST

TAX INCENTIVES

To encourage the use of heat pumps in both district heating and for individual households, the government has slashed electricity taxes for heating and raised those on fossil fuels. As the Danish heat pump market becomes more competitive, Schelle Jensen says some district heating suppliers have begun leasing heat pumps to customers outside a heating network, covering the upfront costs. The government has also begun subsidising the purchase of heat pumps for people living outside the district heating catchment area.

Several smaller Danish towns have begun to gain experience with the use of heat pumps in their district heating, says Martin Lundrup of energy industry trade body Dansk Energi. We need to learn more about using heat pumps in larger cities,” he says and particularly incorporating them into the district heating system. Some larger projects are now in the planning stage. Most recently, the heating supply company in the coastal town of Esbjerg has started the process to install a 50 MW heat pump, along with a 60 MW wood chip fired boiler and 30 MW electrical boiler to replace heat delivered from the existing coal-fired power station, to be retired in 2023. Esbjerg, with a population of 115,000 is the fifth largest town in Denmark.

BIOMASS COMES CLEAN

Biomass, including wood pellets and straw, has been the main driver for taking fossil fuels out of Danish heating, a fuel choice encouraged by changes to energy taxation. Danish lawmakers also recently agreed a further tightening of sustainability requirements for biomass fuel. There has been an increase in biomass imports and that led to the consideration that we should be using our own resources rather than taking them from other countries,” explains Marie Münster, a professor in energy system modelling at the Technical University of Denmark. There were also concerns about how to ensure that biomass is climate neutral.” Although trees and other biomass sources are renewable when consistently replanted, their combustion releases CO2 that takes decades to be reabsorbed in nature’s circular economy. Moreover, the transport of biomass over long distances contributes further to emissions unless the fuel used is from a renewable source. In the short-term, many CHP owners will continue to source biomass that meets the new sustainability requirements, but in the long-term its role may diminish significantly, she says, depending on the future price of sustainable biomass and the potential use of carbon capture and storage (CCS) in biomass-fired CHP plants to prevent release of any emissions.

Heat is easier and cheaper to store than power

SOLAR AND GEOTHERMAL

Denmark is the global leader in solar thermal, but that market leading position still only allows it to satisfy about 2% of heating requirements, much of it by channelling utility scale solar heat into local heating networks. While solar is expected to play a supporting rather than a leading role in supplying heating, its impact could grow. Solar thermal facilities now cover about 1.6 million square meters and potential capacity is placed at about eight million square metres. The next frontier for district heating in Denmark may be underground, in geothermal energy, which due to the relatively low temperature of the resource available in Denmark would need to be used with heat pumps. Denmark’s second largest city after Copenhagen, Aarhus, has teamed up with AP Møller Holding, which controls Danish shipping group AP Moller-Maersk, to explore plans for supplying 100,000 households with geothermal heat. Aalborg, the fourth largest city, is also looking to use geothermal energy. AP Møller Holding estimates that up to 30% of Danish district heating could be provided by geothermal energy.

Data centres, a major and growing consumer of Danish electricity, are also a potential source of heat. Earlier this year, Facebook’s data centre in Odense began supplying low-temperature heat to the local district heating operator, which uses a heat pump to raise the temperature of water heated by servers on the site to a level that can be used in the energy system. The high reliability of electricity supply in Denmark, the 50% renewable energy content of that supply and the country’s suitable ambient climate temperatures has made it a favoured location for data centres. Google and Apple have also set up data centres in the country. The potential for capturing the vast volumes of heat emitted from Denmark’s data centres is largely untapped as yet, says PlanEnergi’s Sørensen. Data centres are huge and there is a lot of excess heat, he says. But using it is often more complicated because the data centres are located near the electricity grid but far away from cities.” Solutions include using liquid cooling for servers rather than air cooling, which would deliver heat at a temperature that could be more easily used in district heating. Looking to the future, the use of electricity to produce hydrogen gas, or a hydrogen-based product, is in some quarters being regarded as a new heat source. Converting electricity to a storable fuel is widely referred to as Power-to-X and combustion of hydrogen for energy produces no emissions at its point of use. If hydrogen is derived through electrolysis and the electricity used is from a renewable source, the gas becomes a clean fuel which could be used in district heating. The cost of the entire process, however, has many experts saying that hydrogen should be re- served as an option for sectors that are hard to electrify, such as heavy transport and industries reliant on very high temperature heat. Equally, the role of biogas in heating is also expected to be limited, although it may play a part in the short term in some individual households where the cost of heat pump replacements is high and in replacing some natural gas in district heating. Biogas is fairly expensive and should not be used for heating in the long term but instead for transport and some industrial processes that are hard to electrify,” says Lundrup.

HEATING A SMALL PROBLEM

In June 2020, 171 of the 179 lawmakers making up the Danish parliament passed the Climate Act that ushered in the 70% emission target for 2030. Changes to energy taxation and new sustainable biomass criteria are also the result of a shared vision stretching across the political spectrum. Cross-party agreement on fundamental principles is normal in Denmark and once policies become law, targets such as decarbonisation of heating are usually met. Since the 1970s, there has been a broad consensus on energy and the climate crisis, which helps provide a predictable environment in which to invest,” says Lauersen. Münster expects the hardest part of decarbonisation in Denmark will involve the transport, industrial and agricultural sectors, rather than heating. We are hoping heating will be a small problem. To a large extent, there are already policies in place to decarbonise it.”

TEXT Heather O’Brian PHOTO Rasmus Hjortshøj, COAST, COBE Architects