Quote from TGregg:
Compressed air is (of course) hugely inefficient. Those of us who studied things like psychics and chemistry instead of woman's studies and 3rd century French poetry (or whatever that was from Groundhog Day) know a formula:
PV=nRT (AKA Perverted Nert in my high school chem class)
where P(ressure) is directly related to T(emperature). In other words, when you are pumping it up you are creating heat. And if you compress it a lot then you create a lot of heat. Wasted heat has another name - lost energy.
Interestingly, when you decompress you are sitting on an icebox - which may or may not be useful.
It is curious that we really haven't figured out a good way to store and release energy. When we do, life will be considerably more interesting.