Abandoned Helsinki oil caverns now heat 25,000 homes for a year

In a groundbreaking project towards carbon neutrality, Helsinki has converted two abandoned oil caverns in Mustikkamaa into the largest heat storage facility in Finland. The facility, completed in 2021, consists of 260,000 cubic meters of hot water stored in the caverns, acting as a giant "heat battery" to regulate energy consumption throughout the year. This initiative marks a unique case globally and is a significant step towards Helsinki's carbon neutrality goal.

The stored heat is equivalent to heating 25,000 one-bedroom apartments annually, reducing the city's carbon dioxide emissions by 21,000 tonnes per year. The hot water, with temperatures ranging from 50 to 90 °C, is filled into the caverns from tap water, a process that took over three months due to the caverns' immense capacity of 320 million liters.

The caverns' charging and discharging capacity is 120 MW, meaning full charging or discharging takes about four days. The stored heat can be used to balance demand peaks, reducing the need for separate natural gas and oil-fired heating plants during winter's coldest days. The project not only meets Helsinki's need for renewable energy but also offers a model for other cities aiming to transition to sustainable energy sources.

By repurposing these oil caverns, the city showcases innovation meeting necessity, contributing to Helsinki's broader strategy of replacing fossil fuels with biomass and waste heat.