A-CAES uses surplus electricity from the grid or renewable sources to run an air compressor. The compressed air is then stored in a big underground tank until energy is needed, at which point it’s released through a turbine to generate electricity that’s fed back into the grid.

Rather than vent the heat generated as the air is compressed, Hydrostor’s system captures that heat and stores it in a separate thermal storage tank, then uses it to reheat the air as it's fed in to the turbine stage, which increases the efficiency of the system. This could prove to be key; compressed air storage systems have typically offered round-trip efficiencies between 40-52 percent, and Quartz is reporting more like 60 percent for this system. //

Hydrostor’s A-CAES also makes use of a closed-loop reservoir to maintain the system at a constant pressure during operation. The storage cavern is partially filled with water and as the compressed air is piped in, the water is forced into a separate compensation reservoir. Later, when the air is needed, the water is pumped back into the air storage cavern, pushing the air out towards the turbine.