It has been said above but is worth pointing out again.
They are using a battery, or in ZPM's case, they are using a gas engine to heat the air. Compressing air fights against the process the whole way. It heats up allowing fewer cubic feet to be stored, it cools as it expands which has to be overcome in order to feed the expansion in the engine.
If you are going to have a battery. . .why don't you just use it to power an electric motor instead of run a heater than runs an air engine? you still lose the 5% in conversion and you lose the %'s associated with heating air and carnot ideals.
I have a PADI scuba license. . .I would much rather haul around a single gallon of gas than a 4,000 PSI tank. 3,000 PSI tanks are heavy enough and more PSI means more materials. 80 Cubic foot tanks weigh 40-50 lbs, they tank they are talking about holds slightly more air but is much heavier. 40 lbs compared to 6 lbs(gasoline).
Even if the motor weighs absolutely nothing to replace my 10 gallon tank you would end up adding weight(over 400 lbs for just the air compared to 60 lbs and 300 lbs of motor).
If you are going to use a KWH for propulsion in a car use it for an E-motor, instead of something complicated.
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