One of the world’s largest seawater heat pumps is to supply climate-neutral energy to some 20 thousand inhabitants of Flensburg in Schleswig-Holstein, Germany’s northernmost state. The city will rely on the federal government to cover about a half of the steep cost.
Just days after one of the world’s largest seawater heat pumps was commissioned in Esbjerg, Denmark, the municipal utilities in Flensburg, Germany ordered a system with the same capacity, the local municipal services have announced. Dirk Thole, managing director of the local utility, has signed a contract worth 70 million euros with the Irish-American company JohnsonControls. The Schleswig-Holstein city is seeking to replace fossil fuels with climate-friendlier energy.
The company is to supply a fifth of the city with carbon-neutral heat by 2027. The nearby communities of Harrislee and Glücksburg are also connected to the grid.
The plan is to place three container modules near the water’s edge at the municipal services area. Each is 13 meters long, 11 meters high and eight meters wide. Several hundred pillars will be driven into the ground for stabilization in the spring.
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Once the heat pump has been installed in mid-2027, it is expected to deliver approximately 3,000 litres of water per second at full capacity. The slightly cooled water will be returned to the fjord shortly afterwards. Even in the merciless winter’s cold, the giant pump is expected to heat the water in the district heating pipes to between 60 and 95°C.
Keeping the back door open
One of the potential obstacles, as is often the case with mammoth green projects, is the steep cost. “Climate neutrality will require heavy investment over the next few years, which we will not be able to do without public funding,“ Stadtwerke Flensburg’s Technical Managing Director Karsten Müller-Janßen told journalists.
„We were one of the first companies in the industry to apply for funding for operating costs back in November 2023 and are now urgently awaiting a decision on funding for a large capacity heat pump. Even though we expect the state support to come through, we had to agree on an exit option in the contract to keep the exit option open in case the financing fails to materialise,” Mr Müller-Jansen said.
In the eastern part of the city, new larger pipes will be required. The utility estimates the total investment in Germany’s first heat pump of this size at €130 million.
The heat pump has a capacity of 60 megawatts, the equivalent of roughly 6,000 individual single-family house pumps. Two additional large heat pumps are expected to bring the city closer to the 2035 climate neutrality target, the Flensburg city council has decided.
“We are proud to contribute to the thermal transformation of the energy industry with our highly efficient technology. Indeed, such future-oriented projects show how it is possible to decarbonise heat supply and become independent of fossil fuels in the future – large-capacity heat pumps are the key to this,” says David Emin, CEO of Johnson Controls Germany.
A giant reverse fridge
Heat pumps use the same principle as your refrigerator – only in reverse. While the fridge draws heat from the inside out to cool its contents, the heat pump extracts heat from its surroundings and transfers it to the heating system.
In Flensburg, heat is extracted from water from the Flensburg Fjord with electricity. To heat the district heating water from 60 to 95°C requires an electrical output of approximately 21 megawatts. The electricity comes from renewable energy sources, so the heat production is completely CO₂ neutral. To achieve this, the new seawater pumps must provide more than 10 000 tonnes of water from the fjord per hour.
The Flensburg project comes five years before the required climate neutrality in Schleswig-Holstein and ten years before the same goal set by the federal government. In the city of just under 100,000 inhabitants, more than 90 percent of households are connected to district heating.
