@burger_jaap Thanks for raising this, I am hoping that the #Varanto storage project would proceed promptly. According to the #VantaanEnergia 2023 Annual Report there was still a complaint on the water economy permit. I couldn't find other updates.

The comparison of 90 GWh capacity with the demand of a mediun sized city is generous, so I would be cautious with that claim.

https://vantaanenergia.s3.eu-west-1.amazonaws.com/uploads/20240403202730/Vantaan_Energia_Vuosikertomus_2023-final.pdf

@jago @janrosenow
The #PitThermalEnergyStorage PTES solution used in Denmark appears significantly cheaper than #CavernThermalEnergyStorage CTES which is popular in Finland.

The 200.000m³ #PTES in Vojens costs about 30 €/m³ whereas #CTES #Varanto in Vantaa costs 200 €/m³.

However, PTES is not pressurised and thus limited to 95°C while #Varanto CTES reaches 140°C, increasing both storage capacity and value of heat.

https://solarthermalworld.org/news/seasonal-pit-heat-storage-cost-benchmark-30-eurm3/
https://solarheateurope.eu/2020/05/19/vojens-district-heating/
https://www.sciencedirect.com/topics/engineering/pit-thermal-energy-storage

The #Varanto seasonal storage facility is featured in @pvmagazine
https://www.pv-magazine.com/2024/04/09/finland-to-host-90-gwh-thermal-energy-storage-system/

The cost of 200 M€ appears high, almost same as annual revenue of @vantaanenergia, but replication potential is huge. Interesting to learn the temperature variation over the year and stratification in the cavern.
Tmax of 140C seems high for seasonal heat storage. Other sites utilising waste heat sources and heat pumps might choose lower storage temperatures, coupled with low-temperature heating grids.