Highview Power’s proprietary cryogenic energy storage technology utilizes air liquefaction, in which ambient air is cooled and turned to liquid at -196 °C (-320 ˚F). The liquid air is stored at low pressure and later heated and expanded to drive a turbine and generate power. It is the only long duration energy storage solution available today that is locatable and can offer multiple gigawatt-hours (weeks) of storage. The CRYOBattery™ has a small footprint and is scalable with no size limitations or geographic constraints, allowing for the deployment of massive amounts of renewables. Highview Power’s cryogenic energy storage plants offer valuable capabilities including voltage control, grid balancing and synchronous inertia that give grid operators the flexibility to manage power and energy services independently.
When you compress a gas, PV=nRT and you lose energy in a higher temperature. When you decompress it, you lose energy as it cools. I doubt it's possible to get beyond 50% efficiency. There's some work done in liquid metal (seriously) batteries. These batteries need to be around 700F (C?) - anyhow, quite hot, you cannot move them when in operation, but because they only operate when the metal in them is molten, once they cool down, they are inert. Basically, it's two metals, separated by a salt which acts as an insulator between them, they claim up to 90% efficiency, and they do NOT degrade like lithium ion does.
TANSTAAFL. Systems with high reliance on mechanical system reliability require high maintenance. Refrigeration pumps don't fix themselves. But, someone got a promotion.
Seems like a good idea if the numbers work.