Something extraordinary is about to be born underground in Vantaa, Finland. Something that could revolutionize the way we heat our cities. It's about Varanto, an unprecedented underground thermal storage facility. It can store up to 90 GWh of energy in the form of hot water: enough to meet the heating needs of a medium-sized city for an entire year. But how exactly does it work? And what are its implications for the future of energy? Let's see together, calmly.
An ambitious project in the heart of the rock
The Varanto project, announced by the Finnish energy company Vantaan Energy, involves the construction of three huge caves underground in Vantaa, about 100 meters deep in the rock. Each cave will measure 300 meters long, 40 meters high and 20 meters wide, for a total volume of 1,1 million cubic meters, including treatment plants.
The world is going through a major energy transition. Wind and solar have become vital technologies in the transition from fossil fuels to clean energy. The biggest challenge of the energy transition so far has been the inability to store these intermittent forms of energy for later use.
Jukka Toivonen, CEO of Vantaan Energia
The caverns will be filled with hot water via two 60MW electric boilers, powered by renewable energy when the cost of electricity is low. The pressure inside the caves will allow temperatures of up to 140°C to be reached without the water evaporating. I'll show you this video first.
An intelligent heating for sustainable heat
Varanto, however, will not limit itself to exploiting excess renewable energy. In fact, the plant will also be able to recover waste heat from industry, thanks to a sophisticated control system that will balance the different energy sources.
When “fully charged”, Varanto will have a total thermal capacity of 90 GWh. A quantity of energy sufficient to cover the domestic heating needs of a medium-sized Finnish city for an entire year.
Most homes in Vantaa, the fourth most populous municipality in Finland, are in fact connected to the city's underground district heating network, which extends for over 600 km. A closed loop system where hot water is pumped through a double pipe to the heat exchangers in each building.
Once the heat has been released, the cooled water is sent back to the production plant to be reheated, in a continuous and efficient cycle.
A turning point for renewable energy and heating
The Varanto plant represents a significant step forward for the large-scale renewable energy heating and storage sector. Finland, already a leader in the production of district heating in relation to the population, thus aims to make its energy system even more sustainable and efficient.
In 2023, the Nordic country has generated 37,3 terawatt hours of district heating,
with over half coming from renewable sources and 14% from waste heat recovery.
With the entry into operation of Varanto, scheduled for 2028, the share of renewables and recovery heat is destined to increase further, reducing the dependence on fossil fuels and waste-to-energy.
A model to replicate on a global scale?
The importance of Varanto goes far beyond the borders of Finland. This pioneering project demonstrates the technical and economic feasibility of large-scale underground thermal storage, paving the way for a possible replication of the model in other cities and countries.
Of course, the construction of a plant like Varanto requires favorable geological conditions, such as the presence of stable and impermeable rocks in which to dig the caves. It also requires large initial investments: Vantaan Energia estimates a construction cost of approximately 200 million euros, of which 19 million have already been allocated by the Finnish Ministry of Economic Affairs and Employment.
But the potential benefits, in terms of emissions reduction, energy efficiency and integration of renewables, are enormous. Not to mention the possibility of creating new jobs and skills in the sustainable energy sector.
Imagine a future where our cities are heated no longer by fossil fuel boilers and power plants, but by heat stored deep within the earth. A future where excess renewable energy and waste heat from industry is captured and stored for use when needed most.
It is the future that projects like Varanto are starting to outline. A future in which energy becomes increasingly cleaner, efficient and democratic, thanks to innovative storage and distribution solutions.
