I feel like they have different applications so they're not necessarily competing. Obviously compressed air systems will never have the energy density of a battery, but they could be much more reliable. It also scales up really easily, and I think that's where the sweet spot is - I've heard of people sealing off caves to make giant air storage tanks for these projects.

"sealing off caves" - would love to see, or hear the facts. Specifically, about safety of the pressure "chamber".

https://caes.pnnl.gov/ - it's an interesting project. Apparently it's more like 'underground caverns' than caves.

I think it is more typically done with old mines. Natural caves are far more complex systems and there are environmental concerns.

you're right - it looks like the caverns being used for experimentation are the result of solution mining for salt.

The charge/discharge efficiency for compressed air is terrible since most of the energy gets wasted as heat. This plus the terrible volumetric energy storage density makes it a nonstarter for most applications.

I think the survival of this will be from them explicitly not trying to compete with batteries, but rather for a different market.