Vantaa, in Finland, is the place where Vantaan Energia is constructing a seasonal thermal energy storage facility known as Varanto. Upon its completion in 2028, it will surpass all existing standards to become the world's largest, boasting a capacity of 1,1 million cubic meters and 90 GWh. The operational concept behind this seasonal thermal energy storage involves storing heat within underground caverns, enabling its utilization for heating buildings through the district heating network as required.

Up to 140 degrees Celsius

Vantaa's bedrock is the place where the seasonal thermal energy storage facility is set to be constructed. This project will involve excavating three caverns approximately 20 meters wide, 300 meters long and 40 meters high, positioned 100 meters below ground level. With a combined volume of 1,100,000 cubic meters, including processing facilities, these caverns will be filled with hot water. The confined space will create pressure, enabling the water to reach temperatures of up to 140 degrees Celsius without boiling or evaporating.

8 million euros worth

Upon completion, the facility will boast a total thermal capacity of 90 gigawatt-hours, equivalent to approximately 8 million euros worth of district heat. This substantial capacity could effectively heat a medium-sized Finnish city or town for an entire year. To put it into perspective, this energy amount is akin to powering 1.2 million electric car batteries.

Hybrid heating system

Varanto enables the maximization of resources by storing previously wasted heat for future use. It marks an advancement towards the implementation of a hybrid heating system. It will select the most efficient generation method available at any given moment, harnessing the full potential of various energy sources. Comparable to a hybrid car, the heat production system will seamlessly transition between electricity and other production forms as needed.

Operational in 2028

With an estimated worth of approximately 200 million euros, the project has secured an additional investment grant of 19 million euros from Finland's Ministry of Economic Affairs and Employment. Construction for the entrance to the storage facility is slated to commence in the summer of 2024, with the seasonal thermal energy storage facility projected to become operational as soon as 2028.