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Project start for Finland's largest underground heat storage facility

Helsinki-based energy utility Helen Oy has begun construction of Finland's largest heat storage facility in the old oil caverns in Mustikkamaa. Demolition work will start soon, and the construction work will start in early 2019. By storing district heat, the rock cavern heat storage facility will reduce Helen's carbon dioxide (CO2) emissions by 21 000 tonnes annually.

In Mustikkamaa there are three underground rock caverns, which were excavated in 1982. They were used for storing heavy fuel oil (HFO) until they were finally decommissioned in 1999. Helen is now converting two connected caverns into Finland’s largest heat storage facility. Procurement is underway, and demolition work in the oil caverns will start in the next few weeks. Construction will start in early 2019, and the heat storage facility will be completed for production use in 2021.

With the Mustikkamaa rock cavern heat storage facility, it will no longer be necessary to use and produce district heat consumed in Helsinki all at the same time thus reducing the operating hours of peak load heat plants.

Heat or surplus heat produced with a high efficiency rate will be stored in the facility when the heating need in Helsinki is not at its highest. The heat of the storage facility can be used throughout the year. Especially in the winter, it may not be necessary to start up heating plants operating on oil or gas. The heat storage facility therefore allows reduction in the use of fossil fuels. The use of renewable fuels and CHP electricity will also be increased at the same time, said Päivi Saajoranta, Project Manager, Helen.

Based on computational comparisons with oil, the heat storage facility will reduce the use of fossil fuels by 1 million litres of oil per year. As a result the Mustikkamaa heat storage facility will decrease Helen’s fossil carbon dioxide (CO2) emissions by up to 21 000 tonnes per annum. The heat storage facility will provide flexibility to the energy system as it will balance variable heat consumption through charging and discharging.

When discharging the heat of the storage facility, the heat can be utilised as such in the form of district heat. The effective water volume in the heat storage facility is 260 000 m3.

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