In the fire service we use 4500psi in aluminum carbon wrapped cylinders for self contained breathing apparatus. A single cylinder 8" by 22" holds enough air for 45 min - 1 hour depending on your degree of exertion. The cylinders are tough, withstanding high temperatures and shock loads. They are also very expensive at $2400.00 each. We have a big honking 220V 3 phase compressor that can fill a bottle in about ten minutes (these bottles have to be filled slowly due to heat build up). The lights dim for blocks around when it is turned on, so I have serious questions weather this car will save any energy.
Unless there is some useful way of harnessing the heat given off in compression, the system is going to be horrendously inefficient.
How about the onboard electrical? Headlamps, radio, power seats, windows, etc... I guess some of those could run off pneumatics; windows down....psssssshhhh....like Star Trek - that would be cool.
Seriously - this is like electric cars and hydrogen power - it's a liberal guilt shifting thing, its psychological. As long as the device I'm using is "green"; not burning fuel or emitting wastes, then I am doing good. Let someone else fire up a coal burning power plant to produce power to run the air compressor to fill my tanks, they are bad.