There's some secret magic going on using moisture and phase change to drastically up the efficiency and storage capacity. It's not just a simple compressed air

There's some secret magic going on using moisture and phase change to drastically up the efficiency and storage capacity. It's not just a simple compressed air system which, as you noted, doesn't work. No idea if their current system will work or not but it's complicated enough that they've spent 7 years trying to get it right.