There are couple out there, summarized here [0] - compressed air cavern - molten salt - regenerative crane - pumped hydro - inclined rail [0] https://www.

There are couple out there, summarized here [0] - compressed air cavern - molten salt - regenerative crane - pumped hydro - inclined rail [0] https://www.nytimes.com/2017/06/03/business/energy-environment/biggest-batteries.html https://www.nytimes.com/2017/06/03/business/energy-environme...