Air of uncertainty

I was very interested in the points Henry Ditmore made in 'Let's be optimistic' (

) promoting the possible use of compressed air (CA) in commuter vehicles.

Although not a sensible way of converting the heat/electrical energy of power stations into mechanical energy for the CA vehicle — due to the large heat loss during air compression — the letter does highlight a very important principle.

That is, a CA cylinder can hold as much useful energy as a battery of similar weight.

If the physical volume of the CA cylinder was also similar, Mr Ditmore may be missing something far more important about CA power than merely powering a small commuter vehicle. I wonder if you can guess what it is.