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Cavern Thermal Energy Storage

We are planning to build a Cavern Thermal Energy Storage in Kuusikonmäki in Vantaa. Thermal energy storage is a noteworthy way to store energy. It plays an essential role in Vantaa Energy’s transition to zero-emission energy production.

We are planning  to build the world’s largest seasonal thermal energy storage facility in Kuusikonmäki, Vantaa, to store renewable energy from solar, wind, waste heat and other sources. The energy will be stored in hot water.

Storing thermal energy enables the waste heat during summer and the surplus heat generated from waste-to-energy to be stored during periods of low heating demand for use during the cold winter season when heating demand is high. It allows flexibility between consumption needs and production.

Thermal energy storage plays an important role in the fossil-free energy system of the future.

Preliminary planning phase
Year of completion
Est.  2028
90 GWh – corresponds to the annual heat consumption of a medium-sized Finnish city


1 000 000 m3
Discharging capacity
200 MW

Storing energy is one of the biggest challenges in the energy transition

Storing energy is one of the main challenges for energy systems in the transition to variable renewable energy production: wind and solar power. Thermal energy storage is an important way of storing energy and will play an essential role in Vantaa Energy’s transition to zero-emission energy production.

The renewable energy stored in a seasonal thermal energy storage and the stored surplus heat from waste-to-energy can replace the use of natural gas during peak heating demand periods in winter.

The significance of storing waste heat in the seasonal thermal energy storage is emphasized: surplus energy from one place can be used elsewhere. Recycling waste heat increases resource efficiency.

How does it work?