[syllable_studio]

You can in fact! Pumped hydro is already the cheapest form of energy storage - about 95% of all energy storage is pumped hydro. We can't build more pumped hydro because it's not feasible to build enough dams. (We've used up the best locations)

The US Gov has studied plenty of research showing that underground pumped hydro is cost effective and obviates the need for dams. (See my white paper here: https://github.com/syllable-hq/uphs-feasibility-study)

So startups like Gravitricity (and Terrament, my startup) are innovating on what is already well-researched territory.