Underground gravity energy storage

[pidcon]

There seems to be an increase in startups working on underground gravity energy storage in 2020. All of them have different designs but similar goals: to save the world. Also, there's the mountain gravity energy storage. Anyone with experience in this area care to comment on their commercial viability?

https://www.gravitricity.com
https://www.terramenthq.com
https://heindl-energy.com
https://www.storage-lab.com
https://energyvault.com

[iMo]

The "gravity storage" is rather old invention, working all around world..
https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
The implementation may vary, but still the same principle.

[Marco]

Everything with winches and cables seems to me to have too much wear and tear. On top of that everything which requires massive amounts of excavation has a lot of up front expenditure, even more than pumped hydro.

IMO pumped hydro, deep sea vacuum pumped hydro and hydrogen storage in gas fields are the only viable TWh scale storage technologies.

I find the deep sea vacuum pumped hydro most exciting, you don't even have to pump sea water with all its corrosion problems. You can just fill the sphere with normal water and pump it into a temporary bladder.

PS. I call it vacuum pumped hydro because it's easy to get the mistaken impression the water is displaced with high pressure air ... which would have awful efficiency.