[effie]

Another completely misleading article on gravity batteries. All the solid weight stuff is bunk, probably designed to suck out money from naive investors / corrupt state officials. Moving solid weights gives only a very small electric power, so building the proposed solid weight batteries gives units of MW at most, which is uneconomical. Unless it transports a large lake of water up and down a hill like in pumped-storage hydroelectric plants, and can provide tens or hundreds of MW. Such installations are very expensive to build today, because all the low-hanging fruit options seem to have been already built.

[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.

[ben_w]

These kinds of gravity batteries worry me a little, because when I've seen the economics, they actually look pretty decent… and yet, that economic calculation ignores the other impacts, like them being terrible energy density and thus needing absurd volumes dedicated to them.

Most proposals are even worse, as they suggest concrete rather than sand. The monetary cost works out even then, but concrete production currently emits CO2, and the combination of that with the low energy density means they'd have to run for around a century to only be as bad as fossil fuels.

[out_of_protocol]

The best option i know of for a mine is compressed air, and there some storages like this already built and operational. Just seal mine/cavity/empty oil well/etc and pump air in. There are some loses on friction, heating-from-compression but overall good economically speaking

[RGamma]

> Unless it transports a large lake of water up and down a hill

https://gravity-storage.com/ are trying to make compact hydroelectric plants by putting weight on the fluid. Wish someone would give them loads of money :/

[imtringued]

Gravity batteries are so appealing, until you calculate the cost per kWh. Any weight that you have to manufacture is already too expensive and you want manufactured weights since you want your weights to be as dense as possible and not just made out of compressed dirt.