TIL that apparently Compressed Air Energy Storage (CAES) has the lowest cost of any method of energy storage? "Techno-economic analysis of bulk-scale compressed air energy storage in power system decarbonisation" (2021) https://www.sciencedirect.com/science/article/pii/S030626192... https://www.pv-magazine.com/2022/07/21/compressed-air-storag... :

> They found the former has a considerably lower Capex and a payback time of only two years. [compared with Lead Acid batteries]

I wouldn't thought that a Gravity Battery would've been more efficient than compressed air: https://en.wikipedia.org/wiki/Gravity_battery

Also TIL about geothermal heat pump energy storage: https://techxplore.com/news/2022-09-geothermal-ideal-energy-... :