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.

First, they restricted code search without logging in so I'm using sourcegraph But now, I cant even view discussions or wiki without logging in.

It was a nice run

Stumbled at this while exploring small web. Not sure if it belongs here but however they are living is pretty solarpunk

From about us:

Hundred Rabbits is a small artist collective. Together, we explore the planned failability of modern technology at the bounds of the hyper-connected world. We research and test low-tech solutions and document our findings with the hope of building a more resilient future.

We live and work on a 10 meter vessel called Pino, we have sailed around the Pacific Ocean and realized how fragile the modern-day computing stack was. Living in remote uninhabited parts of the world has offered us a playground to learn how technology degrades beyond the shores of the western world.