Finnish energy firm Fortum has commenced operations at its large-scale heat pump plants Kolabacken, Kirkkonummi, and Hepokorpi, Espoo, that will utilize excess heat from two Microsoft data centers currently under development.

In the interim, the plants will produce district heating services through heat pumps, which use ambient air as a heat source, and electric boilers. Waste heat from the Microsoft data centers is expected to begin step by step next year, in line with Microsoft’s construction and commissioning schedule.

“The launch of sites is the result of many years of determined work,” said Peter Strannegård, EVP, renewables and decarbonization. “It started seven years ago when our colleagues set out to find a data center partner to implement a ground-breaking excess heat offtake solution, the largest in the world, together with us. It is now becoming reality thanks to the remarkable cooperation between Fortum’s committed experts, Microsoft, the cities of Espoo and Kirkkonummi, Caruna, Fingrid, and all the partners who were committed to this vision.”

Both heat pumps are being built adjacent to the heat pump sites. The initiative was originally announced in 2022, with the data centers expected to support its Finland cloud region, with 75 percent of the data centers’ waste heat expected to feed the district heating system.

According to the company, as new phases of the data centers are completed, increasing volumes of waste heat will be available for the district heating customers. When completed, the heat reuse project will be the biggest to be deployed in the market to date.

The heat pump plants include 40 air-to-water heat pumps, 72 water-to-water heat pumps, producing upwards of 180MWh of district heating, 200MW of electric boiler capacity, and 800MWh of thermal storage capacity. The heat pumps cost an estimated €225 million ($264.8m) to construct.

“Once fully implemented, data center waste heat is expected to cover approximately 40 percent of the total yearly two terawatt-hour district heat demand of the 250,000 heat users in the area,” said Strannegård.

Microsoft has signed several district heating deals over recent years. In addition to the Fortum deal, last month, the company signed a heat reuse deal with Danish heat transmission firm VEKS and Denmark’s largest district heating company, Høje Taastrup Fjernvarme, to supply waste heat to a local district heating network in Høje-Taastrup, Denmark.