Solarpunk

I have been following them for a few years and they are making some slow and steady progress

From their page: As the world generates more electricity from intermittent renewable energy sources, there is a growing need for technologies which can capture and store energy during periods of low demand and release it rapidly when required.

At Gravitricity we are developing innovative, long-life, underground technologies which store energy safely and deliver it on demand at a lower lifetime cost than current alternatives.