The world’s largest demonstration plant for a new kind of renewable energy storage is up and running in the west of the China. Called liquid-air energy storage (LAES) the plant uses renewable electricity to compress air to extreme densities until it turns to liquid. It can then be rapidly released to power a turbine and discharge that green energy back into the grid.
400MWh is the size of the one being planned in Vermont, which would have been the largest commercial system if the states had actually built it. If you follow the link in the article to the story about that one it gives a range of cost per Wh comparing this to hydro storage and lithium ion.