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Massive heat pump project to transform former coal plant site
Mannheim, Germany, will soon host one of the world's most powerful heat pump systems, drawing water from the River Rhine to supply district heating for approximately 40,000 homes. The €200 million ($235 million) project, led by energy company MVV Energie, will repurpose the site of a decommissioned coal power plant.
Engineering on an unprecedented scale
The system's intake pipes, measuring two meters in diameter, are large enough for an adult to walk through upright. Felix Hack, project manager at MVV Environment, stated the pumps will extract 10,000 liters of river water per second, harvesting thermal energy before returning the water to the Rhine.
Two heat pump modules, each with a capacity of 82.5 megawatts, will combine for a total output of 165 megawatts-enough to power the district heating network. Logistical challenges, including transporting oversized components through Mannheim's streets or via the Rhine, remain under evaluation.
"We're not sure yet whether the equipment will arrive by road or river," Hack said.
Competition and innovation in large-scale heat pumps
The Mannheim project enters a competitive landscape, with German rival Everllence developing an even larger system in Aalborg, Denmark. That 176-megawatt installation, slated for 2027, will use four 44-megawatt units to meet nearly a third of the town's heating demand.
Alexandre de Rougemont, a representative from Everllence, acknowledged the rivalry but emphasized the shared goal of decarbonizing urban heating. "It is a competition, yeah," he said. "We're open about it."
Heat pumps function by compressing refrigerants to amplify ambient heat from air, water, or ground sources. While residential heat pumps operate on a smaller scale, district systems like Mannheim's serve entire cities through extensive pipeline networks.
Environmental safeguards and economic considerations
MVV Energie has implemented multi-stage filtration to prevent harm to aquatic life, and modeling indicates the system will raise the Rhine's average temperature by less than 0.1°C. Despite the high upfront costs-approximately €500,000 per megawatt for equipment alone-proponents argue the long-term benefits outweigh expenses.
Veronika Wilk of the Austrian Institute of Technology highlighted the flexibility of district heating systems, noting that operators can adjust the number of active heat pumps based on seasonal demand. "Heat pumps and district heating systems are a great fit," she said.
Global trends and future prospects
Cities worldwide are adopting large-scale heat pumps to reduce carbon emissions. Helsinki, Finland, is overhauling its 1,400-kilometer district heating network, integrating heat pumps, biomass burners, and electric boilers to serve 90% of the capital's buildings. Timo Aaltonen of Helen Oy explained that electric boilers, though less efficient, provide cost-effective backup and grid-balancing capabilities.
The UK lags behind continental Europe in large heat pump adoption but is exploring opportunities in post-industrial areas. Keith Baker of Glasgow Caledonian University identified disused mines as potential heat sources, citing their stable underground temperatures.
The Mannheim project is scheduled to begin construction next year, with full operation expected by the winter of 2028-29.
