Vantaa Energy, an energy supplier in Finland, has announced the upcoming construction of an underground seasonal thermal energy storage facility.
The seasonal thermal energy storage facility will be built in Vantaa, Finland’s fourth-largest city, which will be the largest in the world. The innovative technology, called Varanto, will use underground caverns to store heat, which can then be distributed through the district heating network to heat buildings when it’s needed.
In Finland and other Nordic countries, heat consumption varies significantly between seasons. Heat consumption in the summertime is only about one-tenth of the peak load consumption during the cold winter months. The possibility of storing cheap and environmentally friendly waste heat from data centers, cooling processes, and waste-to-energy assets in underground caverns is a revolutionary innovation in terms of the energy transition.
The use and distribution of stored heat is ideally suited for Finland’s and other Nordic countries’ general district meeting network, to which the majority of properties are automatically connected.
The seasonal thermal energy storage facility will be built in Vantaa’s bedrock and consist of three caverns. These caverns will be quite large, measuring about 20 meters wide, 300 meters long, and 40 meters high. They will be filled with hot water and pressurized to allow the water to reach up to 140 degrees without boiling or evaporating.
The total volume of these caverns, which includes process facilities, is about 1,100,000 cubic meters. The volume of Varanto can be illustrated using a concrete comparison: the underground seasonal thermal energy storage facility is physically almost as large as two Madison Square Gardens.
“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. The biggest challenge of the energy transition so far has been the inability to store these intermittent forms of energy for later use. Unfortunately, small-scale storage solutions, such as batteries or accumulators, are not sufficient; large, industrial-scale storage solutions are needed. Varanto is an excellent example of this, and we are happy to set an example for the rest of the world,” says Vantaa Energy CEO Jukka Toivonen.
The total thermal capacity of the fully charged seasonal thermal energy storage is 90 gigawatt-hours. That’s enough to heat a medium-sized Finnish city for as long as a year. To put it into perspective, this amount of energy is equivalent to 1.3 million electric car batteries.
“Two 60-MW electric boilers will be built in conjunction with Varanto. These boilers will be used to produce heat from renewable electricity when electricity is abundant and cheap. Through the intelligent control of Varanto, electricity generation, waste heat, and district heating, Vantaa will receive a hybrid system that will enable us to take full advantage of the different energy sources. Our heat-producing system will work like a hybrid car: alternating between electricity and other forms of production, depending on what is most advantageous and efficient at the time,” notes CEO Toivonen.
The new seasonal thermal energy storage facility could be operational by 2028. The project cost is estimated to be around 200 million euros, and it has already been awarded a 19-million-euro investment grant from Finland’s Ministry of Economic Affairs and Employment. Construction of the storage facility’s entrance is expected to start in the summer of 2024.
District heating is the most popular form of heating for buildings and homes in Finland. This is mainly due to the underground district heating network that most properties are connected to. In Vantaa alone, there are over 600 kilometers of underground district heating networks, and around 90% of residents live in a home heated by district heating.
Finland is one of the leading countries when it comes to district heating. The country produces the largest amount of district heat per capita in the Nordic region. District heating in Finland works by using the thermal energy produced in local power plants to heat buildings and homes through a closed network of hot water pipes. The hot water is circulated to the buildings, and the water that has released its heat is returned to the production plant for reheating.
District heating networks use heat exchangers to transfer heat to the building, so the district heating water itself does not circulate in the heating networks of the buildings. In 2023, Finland produced a total of 37.3 terawatt-hours of district heat, with renewable heat sources accounting for 53% and waste heat for 14%.
District heating is an environmentally sustainable option for a number of reasons. One of the advantages of district heating is that it is produced locally and is close to the heat users. The energy that flows through the district heating network is as environmentally friendly as the generation forms connected to it. New forms of production and innovative technologies can be integrated into the district heating network as production methods evolve, making it highly adaptable.
