A seasonal thermal energy storage will be built in Vantaa, which is Finland’s fourth largest city neighboring the capital of Helsinki.
The total thermal capacity of the fully charged seasonal thermal energy storage is 90 gigawatt-hours. This capacity could heat a medium-sized Finnish city for as long as a year. Broken down into smaller energy units, this amount of energy is equivalent to, for example, 1.3 million electric car batteries.
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 summer 2024. The seasonal thermal energy storage facility could be operational in 2028.
I think it depends. I am really no expert in costs for energy storage and it would really be interesting to see if this projects tackles high energy costs in the long run and in which way. But if I compare the costs with the costs of building this storage and costs of highways construction in Europe, just to put it in some perspective, it does not seem to be much money.
https://www.worldhighways.com/news/european-highway-construction-costs-evaluated
The information is old, but this sum would roughly buy you 20km Highway in Slovakia. Which is not much.