[oconnore]

Density isn’t always that important, for example the Huntorf Plant uses a gigantic underground cave to store 800+ megawatt hours of energy.

http://www.fze.uni-saarland.de/AKE_Archiv/AKE2003H/AKE2003H_...

https://en.m.wikipedia.org/wiki/List_of_energy_storage_proje...