Helsinki converts old oil caverns into massive underground heat storage system
Helsinki’s utility Helen has filled two former oil caverns with 260,000 m³ of hot water, creating a seasonal heat battery that can supply warmth to about 25,000 homes.
In a pioneering effort toward carbon neutrality, Helsinki’s municipal utility Helen repurposed two disused oil caverns beneath Mustikkamaa into a large-scale heat storage unit. Beginning in late 2020, the caverns were filled with 260,000 cubic metres of water heated between 50 °C and 90 °C, forming a “heat battery” capable of delivering 120 MW of thermal power for up to four days at full capacity. The stored energy, equivalent to roughly 11,500 MWh, can warm about 25,000 one-bedroom apartments for a full year, allowing the city to avoid starting auxiliary natural-gas or oil plants on the coldest days.
Helen estimates the project will slash its annual carbon dioxide emissions by 21,000 tonnes. Built in partnership with Skanska, the facility integrates with Helsinki’s district-heating network and exemplifies a novel reuse of legacy industrial infrastructure.
Why it matters
The project shows how repurposing old infrastructure can cut emissions and improve energy reliability in cold climates.
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