Originally Posted By: kschachn
It is not better than electric, the energy density of compressed air is even lower than a lead-acid battery (which is dismal compared to a hydrocarbon fuel). Modern lithium batteries are much more efficient.
Plus compressing the air takes a lot of energy.
Take the cylinders at a foot diameter and 10 feet long, and at the advertised 4,300psi (29MPa ???)
Adiabatic expansion of this gas to atmospheric yields 36MJ of energy...about equivalent to a litre of gasoline.
Given that there's a point in the depressurisation of the tank that there's no pressure to drive the cylinders, then much less.
Anyone who has pumped up a bike tyre knows how hot things get during compression, all of which is wasted energy when you let it cool back down in storage cylinders before decanting...compressing it to 4,300psi takes lots of intercooling, and therefore more energy wasted could easily be 3-5 times the amount of energy that you get out the other end.
Yet another imaginative boondoggle that will suck up naive investors, and through legislators, taxpayers money.
(as an aside, "refilling" from a gaseous phase cylinder is a pain...take a working tank of volume 1, and a storage tank of volume 10...connect the empty tank to the storage tank, and both tanks end up at 90% pressure...you don't fill the empty tank, and are stuck with less pressure for the next fillup. When we get hydrogen deliveries at 3,000psi, the tanker leaves at nearly 1,000 for the trip home)