Vantaa started digging a massive 300 million euro cave

Machines are now excavating stone and earth at an accelerating pace in Vantaa’s Kuusikonmäki. In the mining that started on Monday, more than one million cubic meters of ore will be moved out from under Ring III, when Vantaa Energy build the world’s largest seasonal heat storage facility in Kuusikonmäki in terms of size and capacity – Reserve.

Excavation takes about three years. It should be ready in 2029 at the latest, when Varanto would be put into use. Tap water is stored in the warehouse, the temperature change of which can be stored energy with the help of district heating.

The approximately 300 million euro project represents a huge change in the Finnish energy system, but in this case, above all, in the district heating system. Heating seems to be happening more in a few years now than has happened in many years.

“That’s exactly what I saw,” says Vantaan Energia’s business director Kalle Patomeri“For several years now, we have been looking for a solution to how we can take care of heating in a big city without burning traditional fossil or even biofuel.”

The need for heating can increase tenfold during the year

The challenge is huge, because the biggest problem for cities and towns is to cope with the peak heating consumption situation caused by the harshest winter frosts. The matter can be put into perspective in such a way that in reality the need for heating can increase more than tenfold from summer to extreme cold, even though the electricity consumption only doubles.

The volume of the 1.1 million cubic meters of thermal storage now being built in Vantaa can be compared to the situation in the whole country. In the latest statistics of the energy industry, different companies have a total of about 409,000 cubic meters of thermal storage of different types. Their combined maximum capacity is 26.2 gigawatt hours. The maximum capacity of the reserve is 90 gigawatt hours.

“The amount can be compared to Varanto’s capacity being sufficient for the heating needs of a medium-sized city for a year. 17 Varantos would be needed for Vantaa’s needs,” Patomeri smiles.

According to Patomere, many things have had time to change in the planning of the project that started 4.5 years ago.

Mining and construction of the reserve was supposed to start a year ago. The price estimate for the investment was previously EUR 200 million. “This cave is designed to be used for the next hundred years.”

“Originally, this was supposed to be a clean seasonal storage of heat, where the water would have been at 100 degrees, as it is in all other heat storages.”

Front energy hybrid system

“Now that it is possible to raise the water temperature up to 140 degrees, this becomes a flexible element for heat and electricity. This enables us to operate in the heat market of the capital region, when we are connected to Helsinki, Espoo, Kerava and Tuusula.”

Flexibility means that with the intelligent control of Varanto, electrical production, waste heat and district heat, a system is created in which Vantaa can more precisely optimize which production form heat is produced at any given moment.

Patomeri is talking about a hybrid system, where heat pumps, electric boilers, waste heat and large warehouses must be made to work together as efficiently as possible.

“If you think about euros, one-third of Varanto’s revenue comes from storing heat in seasonal storage, and two-thirds of the revenue comes from regulating the heat and electricity markets.”

Hyvinkää stores heat in the gravel pit

All energy companies have to think about the same basic questions. Outside the capital region in Hyvinkää Hyvinkää Lämpövoima is currently building on an old gravel lot a huge indoor water pool, with a planned size of 380,000 cubic meters and a storage capacity of 18-20 gigawatt hours.

It is the world’s largest pit thermal energy storage (PTES = Pit Thermal Energy Storage) and at the same time the first of its kind in Finland. The size of the investment is 33 million euros and it will be completed in autumn 2027.

The heat is stored in a gravel pit in a large coated pool with clean tap water. The thermal storage will be equipped with a floating cover structure so that the heat does not evaporate from the pool of water into the air. The heat used in the heat storage comes from industrial waste heat generated in Hyvinkää and its surrounding areas.

Hyvinkää Lämpövoiman Sanna Kytömäki says that the heat storage is a significant part of Hyvinkää’s future district heating system, where heat is produced entirely with waste heat and renewable heat sources.

The investment in Hyvinkää is comparatively clearly cheaper than the investment in Vantaa, which is due to the clearly less demanding construction conditions.

Emeritus Professor of Energy Systems at LUT University Esa Vakkilainen I especially praise the fact that energy storage has moved from hours and days to the scale of the whole year.

“When heat can be transferred from summer to winter, fuel is saved and prices are better kept under control,” says Vakkilainen in the bulletin.

The waste heat of data centers fits this pattern perfectly. Data centers produce heat all year round, and when it can be stored efficiently, we talk about a genuine circular economy.

Water storages are currently the most technically and economically sensible in large solutions. The advantage of water is that they work for sure.

Sand batteries have their own market

According to Vakkilainen, the much talked about sand storages are promising, but still small in size.

Still, they can work and be just the right solution in smaller towns. For example, in Pornais The heat of Loviisa finished in the summer Polar Night Energyn (PNE) developed an industrial-scale sand battery for the Pornainen district heating network. Sand battery was inaugurated in August.

Even though the power of the sand battery is only 1 megawatt and the storage capacity is 100 megawatt-hours, it is still about ten times larger than originally in Kankaanpää in 2022 For Vatanjakoski constructed sand battery. According to Loviisa Lämmö’s estimate, the emissions of the Pornainen district heating network will decrease by about 70 percent with this system as well.

PNE’s sand battery is also trusted in Lahti. Lahti Energia said a few weeks ago investing in Vääksy’s district heating network Upgrade a larger sand battery with a power of two megawatts and a storage capacity of 250 megawatt hours.

The work will start next year and should be ready in the summer of 2027. With the help of the sand battery, fossil emissions from the heat production of Vääksy’s district heating network will be reduced by about 60 percent per year, according to the company’s estimate.

Sand batteries seem to work well precisely as emission reducers in small agglomerations.