Winter heating in Finland’s fourth largest city, Vantaa, will be provided from waste heat stored in underground caverns during the summer months, in an initiative Vantaa Energy says will be the world’s largest seasonal energy store.
The planned thermal energy store will be large enough to heat a medium-sized Finnish city all year round and will be used to heat buildings via an existing district heat network whenever it is needed.
Vantaa Energy explains that in Finland and other Nordic countries heat consumption in the summer time is one-tenth the peak consumption in winter. It wants to store cheap and environmental friendly heat from cooling datacenters, processes and waste-to-energy assets in three caverns excavated from bedrock beneath the city. The caverns, 20m wide, 300m long and 40m high – as large as two Madison Square Gardens – will be 100m below ground level. The caverns will be filled with hot water at high pressure, which can reach temperatures of up to 140 degrees without boiling or evaporating.
“The biggest challenge of the energy transition so far has been the inability to store these intermittent forms of energy for later use. Unfortunately, small-scale storage solutions, such as batteries or accumulators, are not sufficient; large, industrial-scale storage solutions are needed. Varanto is an excellent example of this, and we are happy to set an example for the rest of the world,” said Vantaa Energy CEO Jukka Toivonen. He added, “Two 60MW electric boilers will be built in conjunction with Varanto. These boilers will be used to produce heat from renewable electricity when electricity is abundant and cheap.” The system will alternate between electricity and other forms of production, depending on what is most advantageous and efficient at the time.
The total thermal capacity of the fully charged seasonal thermal energy storage will be 90GWh.
The €200 million project has already been awarded a €19 million investment grant from Finland’s Ministry of Economic Affairs and Employment. Construction of the storage facility’s entrance is expected to start in summer 2024. The seasonal thermal energy storage facility could be operational in 2028.