The plant in Värtan, north of central Stockholm, looks like an oversized parking deck. It is, in fact, a heat-pump array.
What is happening inside it is the most underreported piece of European energy news of the decade. Six high-temperature pumps, fed by Baltic seawater that has been pre-warmed by data-centre exhaust, supply 240 megawatts of district heat. Two more are under construction.
Why Stockholm and how Hamburg follows
Stockholm has the political consensus and the cold-water access. Hamburg has the gas legacy and roughly 2.5 million more people to keep warm. HanseWerk’s pilot in Wilhelmsburg has begun retrofitting 9,000 flats from gas-condensing boilers to centralised heat-pump arrays, running off the Elbe and a sliver of the city’s grid surplus.
The new procurement question
For decades, the cost question was: how much does a heat-pump cost compared to a gas boiler? In 2026, the question is different: how do we replumb a 1960s residential block to take district-network water at 70°C instead of 90°C? The math now favours the pump in basically every European latitude north of Lyon.