[donquichotte]

My thoughts exactly. It makes the engineer in me go mad if I see projects like Energy Vault [1] getting massive funding that could be used to try and develop technologies that make sense. Thankfully there are some people who see through the charade [2].

If you are into this thing and looking for an even more stupid idea to store energy, I present to you the StEnSEA [3]. Rolls right off the tongue, right? It is a hollow concrete sphere that is lowered to the bottom of the lake. Pumps then remove water from it, creating a vacuum. Letting the water back in and using the pumps as generators, the energy is reclaimed. Curiously absent from all documentation of this project is the amount of energy stored. I did some back of the envelope calculations a while back and it is 3.8kWh, for a multi-million-euro prototype!

[1] https://www.energyvault.com/ev1

[2] https://www.youtube.com/watch?v=iGGOjD_OtAM

[3] https://www.iee.fraunhofer.de/de/projekte/suche/2013/stensea...

[concordDance]

> 3.8kWh

That seems very low. Their website mentions 20 Mwh+.

Though my back of the envelope agrees with yours.

[donquichotte]

If I understand it correctly, ~20MWh is for the full size model at 700m depth and with a radius of 15m (prototype radius is 1.5m and it is located at a depth of 100m).

And building concrete spheres that can withstand the pressure of a 700m water column is probably an interesting design challenge on its own.