Repurposing waste heat from Power-to-X for district heating requires coordination to maximise these synergies
WASTE NOT WANT NOT Recovering waste heat from electrolysis processes provides a low-carbon source for district heating operators
SCANDINAVIA TRIALS Several PtX projects across Finland, Denmark and Norway have partnered with district heat network operators
KEY QUOTE The equipment or components required to integrate a green hydrogen production facility with a district heating network are relatively simple to implement
Losses happen when energy is converted from one form to another. This is fundamental. Power-to-X (PtX) plants consume electrical energy to generate chemical energy and heat. The resulting hydrogen molecules can be the building blocks to replace fossil fuels used in heavy industries, chemical processing and fuels for heavy transport, shipping and aviation. But often the heat is wasted.
The EU is expected to produce ten million tonnes of renewable hydrogen to meet part of its demand by 2030. Since around 25-35% of electrical energy supplied to PtX facilities is transformed into heat in the electrolysis part of the process, while other associated activities like compression also produce heat, there is a big opportunity to reuse all that hot air.
According to a Danish study by Euroheat & Power, a trade association, six gigawatts (GW) of installed PtX capacity would produce enough surplus heat to cover up to around 20% of district heating demand.
“Green” hydrogen—and derivative products like ammonia—are more expensive to manufacture than “grey” or “blue” hydrogen. Securing revenue streams for heat and oxygen, both byproducts of electrolysis, enables green hydrogen developers to improve the return on investment of these plants. Ramboll, a Danish engineering firm, estimates that heat sale revenues could be up to 5% of a PtX facility’s total income.
Erik Rynning from Aker Horizon, a Norwegian PtX project developer, says the company is exploring reusing waste heat in district heating or industrial applications to improve the resource efficiency of its PtX projects, add an additional revenue source and enhance circularity.
Municipalities and district heating companies are also interested in PtX as they are planning ten years ahead, says Ramboll’s Eva Ravn Nielsen. “A large green hydrogen or PtX project in development nearby could influence how they invest in their district heating networks in future because it is potentially a supplier of low-cost waste heat,” she says.
HEAT TRIALS Helen is building a PtX electrolyser pilot in Vuosaari with the waste heat to be used in the company’s nearby district heating network
“From a technical perspective, the equipment or components required to integrate a green hydrogen production facility with a district heating network are relatively simple to implement,” Nielsen says.
The temperature of waste heat is, however, too low for district heating networks and needs to be boosted by a heat pump or electrical boiler. Other equipment such as heat exchangers, connections and some instrumentation, are also required.
Investment in any equipment that integrates the PtX plant with the district heating network for supplying the waste heat is usually borne by the PtX developer, which will also own this equipment.
Meanwhile, the receiving district heating company may need to be able to have control of the heat output, either automatically or manually, via a daily agreement with the PtX developer, as the heat will be one of several sources supplied to the network.
There also needs to be an agreement in place around risk sharing.
PIPE WORK Combining PtX and district heating networks takes advantage of synergies between the technologies
LOCATION, LOCATION, LOCATION
To maximise the mutual benefits, the location of the assets is important. PtX facilities usually need to be located close to supplies of renewable electricity and water. To supply district heating, PtX projects should also be situated near the cities or other urban areas that have these networks in place or with plans to introduce them. This might limit the uptake.
While it will never be possible to integrate all the waste heat from PtX facilities, utilising it where possible will provide an additional opportunity to decarbonise heating and lower costs for consumers in the process.
“There is a case to be made for direction to come from central government that would encourage the siting of PtX plants near urban areas or communities with district heating networks. If a plant is too far away, it would become cost-prohibitive to install the infrastructure to transport the heat from a PtX plant over long distances to the district heating network,” says John Flørning, also from Ramboll.
|Modelling potential of electrolysers for providing heat
Mӓlardalen University published a study that models heat from a 100 MW electrolyser, comparing alkaline and PEM technologies. The modelling is based on the Botnia Link H2 Project in Luleå, Sweden, which is in development.
A large-scale heat pump and a heat exchanger were included in the modelling to integrate the waste heat on the district heating network, while also providing cooling for the electrolyser stack. The study concluded that heat used from either PEM or alkaline systems is price competitive in comparison with other thermal energy sources.
Using hourly data from Luleå Energi, the results showed that 171,770 thermal megawatt-hours (MWhth) can be integrated on the DH network annually with a PEM electrolyser, while 226,220 MWhth can be integrated on the DH annually with an alkaline electrolyser.
The levelised cost of heat (LCoH) for the PEM electrolyser is SEK 0.218/kWhth and SEK 0.23/kWhth for the alkaline-connected system.
With fourth-generation district heating networks, the study predicted the LCoH can reach SEK 0.018/kWth for the PEM system and SEK 0.017/kWth for the alkaline electrolyser system.
In Norway, the potential for waste heat to supply district heating is large as it is rarely used in district heating networks today; waste incineration, biomass and, to a lesser extent, fossil fuels, provide the majority of sources for district heating.
Aker is working with local municipalities and agencies to explore opportunities for using the waste heat from its projects, including district heating. In Rjukan the company is developing a five-megawatt (MW) electrolyser. Aker is part of Circular Rjukan, an initiative that has been established to evaluate the potential to use waste heat and other circular economy opportunities.
“We have, together with Rjukan Business Development (Rjukan Næringsutvikling), been in dialogue with potential companies to look for synergies and business opportunities which may be viable in the future. We can also utilise the heat for district heating of buildings, contingent upon the local community establishing the necessary infrastructure,” says Rynning.
There are no district heating systems at Rjukan, but new residential areas are likely to be planned with district heating systems, he adds.
|PtX projects hooking up with district heating networks
A number of projects that combine PtX electrolysis and district heating systems are underway in Europe, with Scandinavia leading the way:Denmark
PARTNERSHIPS IN FINLAND
In Finland, energy supplier and district heating network owner Tampereen Energia and PtX developer Ren-Gas are laying the groundwork for a district heating integrated electrolyser in Pirkanmaa, southwest Finland.
The project will be sited next to the Tarastenjärvi waste-from-energy heat and power plant, which is operated by Tammervoima, a joint venture between Tampereen Energia and local waste company Pirkanmaan Jätehuolto.
From 2026, when the planned 60 MW electrolyser becomes operational, the waste heat will be recovered and returned to Tammervoima for the district heating network, which supplies more than 5000 buildings and more than 230,000 residents.
Recovering the waste heat from electrolysis improves profitability, according to Jukka Joronen of Tampereen Energia. Tampereen Energia is owned by the City of Tampere and it has strict environmental targets, including ensuring that its heating supply is fully carbon neutral by 2030.
In other projects, Ren-Gas partners with municipal and regional energy companies which also own district heating networks. Its project in Kerava, located 30 kilometres from Helsinki in southern Finland, is sited with Keravan Energia’s bio-combined heat and power (CHP) plant, which will produce 12,000 tonnes of methane, 6000 tonnes of hydrogen and 150 gigawatt-hours (GWh) of heating from a 20 MW electrolyser.
Ren-Gas wants to build a PtX portfolio in Finland by 2030 that will deliver 20% of the e-fuels needed by the heavy road transportation sector and 8% of the Finnish district heating needs. This will replace 2.5 terawatt-hours of district heating produced by fossil fuel burning, the company predicts. Finland has banned the use of coal for energy from 2029.
Energy utility Helen is aiming for its energy production to be carbon-neutral by 2030. Earlier in 2023, Helen closed down its Hanasaari CHP plant in Helsinki. Helen is instead developing a 4 MW PtX electrolyser pilot in Vuosaari, in the eastern district of Helsinki, and the waste heat—about 13,000 megawatt-hours a year—will be used in the company’s district heating network.
A number of homes in Helsinki are already heated by the Vuosaari bioenergy heating plant, which burns wood chips obtained as a by-product of forestry. But by using heat pumps Helen can use different waste and environmental heat sources. The heat that will be produced by the Vuosaari electrolyser will be roughly 60-70°C degrees so the heat pump will boost the temperature to meet district heating requirements.
“Hydrogen [production] will support the electricity network through sector coupling and potential energy storage. The utilisation of waste heat from hydrogen production is also important, as it can save both energy and costs,” Helen’s Tuukka Hartikka says.
In Denmark, which has comparatively high levels of renewables penetration, any excess electricity is absorbed by heating networks installed with heat pumps and electric boilers. In the future, PtX facilities will also be able to absorb excess electricity.
“As heat demand varies throughout the year, with more heat needed in the winter than in the summer, seasonal storage can store some of the heat that is generated by green hydrogen production,” Hartikka says.
Ren-Gas says its PtX portfolio’s approximately 600 MW of electrolyser capacity is highly flexible to changes in electricity consumption, increasing demand flexibility in Finland’s electricity grid.
“For many years to come, buildout of renewable energy is in general the key to decarbonisation of our society. PtX plants will operate fairly constantly but also with a degree of flexibility so that they can capitalise on the lowest electricity prices when there is a lot of renewable generation on the grid,” Ramboll’s Ravn Nielsen says.
TEXT Sara Verbruggen PHOTOS MidJourney/FORESIGHT; Helen Oy
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