Sperra's StEnSea seabed spherical energy storage: Emptying charges sphere, water flowing in generates electricity

https://www.iee.fraunhofer.de/en/presse-infothek/press-media/2024/fraunhofer-iee-and-partners-test-spherical-energy-storage-on-the.html

"prototype: anchor hollow 9 (30 for production model)-M diameter 400-ton concrete sphere at 500 to 600-M depth, 0.5-MW power, 0.4 MWh capacity... 3D concrete printed... end of 2026 at latest... top opening into which pump turbine, will integrated in pipe... total global storage potential 817K GWh... 4.6 cent KWh storage cost, €1,354 investment cost per KW, €158 euros per KWh of capacity, concrete lifetime 50 to 60 yrs, turbines/ generators 20 yrs... short to medium-term scalable storage"