Inside the World’s Largest Thermal Energy Storage Facility

With an estimated completion date of 2028, Varanto — Vantaa’s thermal energy storage facility — will store energy equivalent to that of 1.3m EV batteries

One of the main issues facing reliability of renewable energy sources is its variability. The fluctuating nature of renewables like solar and wind — which depend on the availability of sun and optimum wind power — means it may not be available when needed, or that an excessive amount is available when demand is not high.

This is an increasing issue in geographies like the Nordics, where heat consumption varies significantly between seasons.

In a bid to tackle this issue, Vantaa Energy has announced it will begin construction of a seasonal thermal energy storage facility, the largest in the world.

Called Varanto — which translates as ‘vault’ or ‘reserve’ — the facility will store heat in underground caverns to then heat buildings via a district heating network whenever it is needed.

The need for renewable energy on-demand

The idea for Varanto is borne of the possibility to store cheap and environmentally-friendly waste heat from the likes of data centres, cooling processes and waste-to-energy assets in underground caverns is a revolutionary innovation in terms of the energy transition.

As well as waste heat, the facility also enables the cost-effective storage of renewable energy, boasting the ability to store an amount of energy equivalent to 1.3 million EV batteries, enough to heat a medium-sized Finnish city all year round. The project is set to cost €200m (US$217.2m).

“The world is undergoing a huge energy transition. Wind and solar power have become vital technologies in the transition from fossil fuels to clean energy,” Vanta Energy CEO Jukka Toivonen said, acknowledging how Varanto will play a major role in overcoming the challenge of storing intermittent energy forms for use at a later date. 

Jukka Toivonen, CEO of Vantaa Energy

Construction of Varanto will begin this summer, with a completion date set for 2028. It will be built in Vantaa’s bedrock, made up of three caverns filled with hot water 100 metres below ground level measuring about 20 metres wide, 300 metres long and 40 metres high. Because of pressure created in these caverns — which have a cumulative volume of 1.1m cubic metres — the water will be able to reach temperatures of up to 140°C without boiling or evaporating.

Why Finland is a leader in innovative energy and storage

Finland has emerged as a leader in innovative energy and storage thanks to many factors, including its strong focus on research, supportive policy environment, technological expertise, collaborative ecosystem and favourable market conditions. 

As well as positioning the country as a hub for energy innovation, this helps the overall standings of the Nordics as a region, which includes Sweden, Norway, Denmark and Iceland.

The International Energy Agency (IEA) also declares that Finland’s nuclear and renewable power strengths provide a solid foundation for reaching its ambitious climate targets.

This is also thanks to its early adoption of smart grid technology and related technologies such as household-specific, remotely readable, accurate electricity consumption metering and real-time power grid failure monitoring. The International Trade Administration says this has led to improved energy use information and enables Finland to move towards the next step of smart grid technologies to meet the increased volume of small-scale generation, customer-level energy storage, EVs and controllable. As a result, Finland is able to put consumers at the heart of its energy and efficiency measures.


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