The background for Denmark’s leading position in the world concerning the spread of district heating is that covering the heating needs of buildings by connecting to district heating has been part of Danish society for more than 100 years- indeed, for almost 120 years.
This article provides insight into the benchmarks for further development toward a CO2-neutral district heating system in Copenhagen of 2050. A quick historical overview of the development of district heating in Greater Copenhagen from the beginning of 1903 until today is shared in the article “District heating in Greater Copenhagen – history and status 2023.”
By Lars Gullev, Senior Consultant, VEKS
What does the district heating system in Greater Copenhagen look like today?
The capital’s district heating system today covers a heat demand of 38 PJ (2020 figures)-of which heat production from waste energy plants covers approx. 32% of the heat demand. The heat demand of 38 PJ corresponds to about 25% of the total heating demand in Denmark.
The heat production is dominated by large central cogeneration systems on waste and sustainable biomass, which account for around 2,150 MW of base load capacity. In addition, approx. 50 MW heat pumps were established recently, and surplus heat is utilized from the industry and wastewater systems.
In addition to this, there is a peak and reserve load capacity of approx. 2,300 MW and two heat accumulators (2*22,000 m3 + 25,000 m3) of a total of 2700 MWh. tip and reserve loads are mainly based on natural gas and oil. In recent years, however, several electric boilers have been established for peak and reserve load heat production.
Briefly described – this is a district heating system based on large central production units – but the future looks different.
Therefore, the district heating companies HOFOR, CTR, Vestforbrænding, and VEKS decided four years ago to prepare scenarios – with associated analyses- to develop the district heating system in Greater Copenhagen by 2050.
Starting the analysis, it soon became clear that the future district heating system in the metropolitan area would be changed from being based on key production units to a system with more decentralized production units. It would also be characterized by a larger system integration with the electricity system than we know today.
“Future District Heating Supply in the Greater Copenhagen Area 2050”
The four district heating companies, HOFOR, CTR, Vestforbrænding, and VEKS, completed phase Four together in the dynamic development project “Heat Plan Capital” to ensure a shared vision. The level of ambition compared to the previous phases was turned up, and at the same time, the project changed its name to “Future District Heating Supply in the Metropolitan Area 2050”.
The primary purpose of the shared vision was:
- To build a unified vision-based frame narrative by 2050, supporting a future competitive and green district heating supply – including searching for strategic challenges which could prevent the fulfillment of the vision and finding ways to deal with them.
- To develop shared ideas for options and ways of action by 2025 and 2030 concerning fulfilling the 2050 vision and frame narrative, thus ensuring a competitive and green future district heating supply.
- To develop a common base that – across the four companies – should support the decisions to be faced in the coming years
- To ensure future decisions with stakeholders (owners, municipalities, customers, etc.) are made on a common base
The analyzes of future technologies, therefore, included large heat pumps, low-temperature district heating, geothermal, CCSU (CO2 catch and storage), PTX, and heat storage.
Large heat pumps
The potential for large heat pumps in the district heating system is considerable. It includes heat sources such as seawater, drinking water, wastewater, groundwater, air, industrial surplus heat, and geothermal.
Based on the heat sources, the theoretical potential for large heat pumps in the metropolitan region’s heat supply was estimated at 2,100 MW by 2050. But when considering the available heat base in the individual distribution networks in the total supply area, the potential was closer to 1200 MW.
Seawater would have great potential as a heat source, but it is an immature technology that must first be matured and tested in the Danish context. At the same time, heat pumps that use seawater will be challenged in efficiency during winter when the water temperature reaches 1-5 °C.
Wastewater as a heat source and air-to-water heat pumps, which use outdoor air as a heat source, have excellent technical potential. Still, for air-heat pumps, there are challenges in providing space for the physically large plants where the outdoor part creates considerable noise.
HOFOR/CTR/VEKS has tested a 5 MW sea/wastewater heat pump established in Copenhagen Harbor for several years.
Surplus heat from the industry
Industrial excess heat, where the heat source usually has a higher temperature, such as 10-25 °C degrees, is often competitive, but the potential is relatively limited according to the analyses. However, there is great potential for using surplus heat from data centers, but it is unclear how many data centers will be established.
With CP Kelco in Køge, VEKS has realized a project to use excess industrial heat by combining heat pumps and exchangers – total utilized power amounts to 7 MW.
Køge Power Plant, owned by VEKS, has established a 1 MW heat pump for using surplus heat from turbine oil cooling and a 13 MW heat pump to utilize surplus heat from flue gas condensation.
Low-temperature district heating
Heat pumps are most efficient when they must deliver heat at relatively low temperatures, which is why it is an economic advantage to place them as close to the distribution network as possible. As required in the transmission network, heat pumps that can deliver heat at higher temperatures are still relatively expensive and untested in Denmark.
If the large heat pumps are to be used economically and technically in the best way, they must be placed close to the district heating network and close to a heat source (e.g., excess heat, groundwater, seawater, or wastewater). This requires reserved space in the metropolitan area and cooperation between energy planning and physical planning in the municipalities.
The analysis has therefore investigated whether switching to low-temperature operation in both the transmission and distribution networks is possible. Today, Tf in winter is typically up to 115 °C in the transmission network and a maximum of 90 °C in the distribution network. In low-temperature operation, Tf is lowered to 90 °C in the transmission network and to 70 °C in the distribution network – in connection with new construction, Tf is reduced further. Tr must follow down.
The analysis shows that it is technically possible to convert to a low-temperature level and to convert the transmission and distribution grids for relatively low costs. However, this requires a lot of additional technical and hydraulic analyzes as well as intensive cooperation between the district heating companies.
Lowering the temperature is also estimated to provide significant savings in heat production costs – around 8% or DKK 250 million per year (€ 33 million/year). At the same time, lower Tf gives a smaller net loss; on the other hand, the network’s transport capacity is reduced by up to 25%. Therefore, it will be even more important to see a temperature drop in connection with future decentralized production capacity placement.
Geothermal heat is a stable and suitable heat source for district heating, and research indicates a sizeable geothermal potential in the underground capital area. The potential is limited by the quantities consumed in the distribution networks, which amounts to 6-700 MW. Since the plants utilize geothermal heat with heat pumps, they will primarily be able to supply heat to the distribution grid, as it will be too expensive to provide heat at the high temperature required in the transmission grid.
In autumn, HOFOR/CTR/VEKS started contract negotiations with the company Innargi regarding establishing geothermal energy in the capital area from around 2030.
Capture and storage of CO2
In the metropolitan area, there are several large point sources for CO2 capture from the combustion of biomass and waste at large cogeneration plants. If CO2 from biomass – or the biogenic part of the waste – is stored underground, this results in negative CO2 emissions. The capture process requires a lot of energy, a large part of which ends up as excess heat that can be used in the district heating system.
Together with five other companies, HOFOR/CTR/Vestforbrænding/VEKS work together in the cluster collaboration C4 – Carbon Capture Cluster Copenhagen – with a vision to reduce CO2 emissions in the capital city area by 3 million tons annually through CO2 capture. Here, the heating companies’ interest is to utilize the excess heat that is a consequence of CO2 capture – and VEKS has entered the first LOI with a heat producer in this regard.
CCS (Carbon Capture and Storage) is an investment-heavy technology, and the costs of establishing and operating CCS are uncertain. For CCS to become economically feasible, the process – either in the form of subsidies or by capturing CO2 from the biogenic part of waste and biomass – must be priced as “negative emission.”
Transport of CO2 to underground storage can be done by truck, ship, or in pipes, and the actual storage can be done offshore or on land-based coastal storage. In connection with the transport, there will be activities that generate surplus heat, which may be interesting for the district heating companies to utilize.
In the spring of 2022, the “Cluster collaboration on CO₂ transport and infrastructure in Greater Copenhagen” was established to initiate work on CO₂ infrastructure and make recommendations to the Parliament about what is needed to develop CO₂ infrastructure in the capital area. In addition to HOFOR, CTR, Vestforbrænding, and VEKS, behind the cluster cooperation were 14 companies, each of which has an interest in Denmark and the metropolitan area achieving the climate goals as cheaply as possible.
In January 2023, the Cluster Collaboration submitted its report outlining the most important recommendations for CO₂-transportation.
As an alternative/supplement to storing CO2, this can be used in a Power-to-X (PtX) process to produce green fuels for heavy transport – trucks and ships – as well as aircraft. This process develops excess heat, but the production of the excess heat can be highly fluctuating, which creates a need for huge heat stores and/or flexible backup heat capacity from, for example, biomass cogeneration/boilers with CO2 capture.
The choice of PtX technology is decisive for the temperature of the excess heat and whether the excess heat supply is stable or fluctuating. The report also concludes that the district heating system in the capital can both deliver CO2 for collection and utilization and absorb and utilize up to 750 MW of surplus heat from PtX processes, provided that multi-string heat production is maintained.
A multi-stranded production mix, as described above, necessitates the establishment of many more large heat storage facilities in the future – either as pond heat storage facilities or in pressurized steel tanks. With the future production mix, it is estimated that it will be profitable to increase the heat storage capacity 3-6 times compared to today’s level in the metropolitan area. Therefore approximately 8,000-24,000 MWh of new dam heat storage capacity and 4,000-8,000 MWh storage capacity in steel tanks must be built on the transmission network by 2050. Today, the storage capacity in pressurized steel tanks is just under 70,000 m3, and a new dam heat storage of 70,000 m3 is being commissioned in early 2023.
It can be challenging to determine what the district heating system in the capital will look like in 2050. Still, the analyzes in “Future District Heating Supply in the Capital Region 2050” indicate the following:
- The current district heating system is robust and can accommodate a more multi-stranded district heating supply, where new technologies can be incorporated.
- The existing fossil solutions, to a certain extent, have lower costs than the green solutions. A complete conversion of the district heating with green solutions is possible. Still, it risks becoming expensive, and therefore the conversion must be done so that the district heating can maintain its competitiveness.
- In scenarios with a large proportion of centrally located production, for example, in the form of PtX, investments in the district heating network may be needed to better utilize heat production from the production locations at the large central plants.
- The difference in the production composition in the scenarios significantly affects the distribution between central and decentralized production. In the scenarios for 2050, between 22% and 65% of the heat is produced decentralized in the distribution areas.
- Sustainable biomass, which has been the key to the rapid phasing out of coal, and in which the heating companies have made large investments, is being challenged by politicians and interest organizations, who question the availability of sustainable biomass. The analysis concludes that a forced phasing out of biomass before 2030 is not technically and economically possible. It will be very expensive for the heating customers if non-depreciated CHP plants are closed, and it will put the security of the electricity supply on hold.
- In all scenarios, biomass use will be reduced both in 2030 and in 2050 as other technologies take over. It is also emphasized that biomass provides flexibility and can supply heat in periods with high electricity prices, just as it contributes to the security of supply in cold months, when, for example, seawater heat pumps can have problems supplying heat.
The “Future District Heating Supply in the Capital Region 2050” project has generated several background reports before the main and summary reports. You will find this material at https://varmeplanhovedstaden.dk/ – unfortunately, only in Danish.
However, one thing is obvious – the future district heating system in the capital area will change from a system based on a few central production units to a system with several decentralized production units. It will be a system characterized by greater integration with the electricity system than we know to date – including utilization of excess heat from the capture and transport of CO2 and heat from PtX processes.
Large district heating systems are, therefore, not something that only belongs to the past but systems that are a prerequisite for us to use our energy resources responsibly in the future.
Find facts about the four district heating companies, HOFOR, CTR, Vestforbrænding, and VEKS, in the article “District heating in Greater Copenhagen – history and status 2023.”