Why not cascade two alternative fuels? Carbon fiber 5000psi 88 cu.ft.
tanks are common now for $600+ but with volume who knows.
This whole alternate drive here is use central electricity and distributed storage of that energy in various forms to drive down energy prices.

India is developing such a duel fuel engine for its air car http://www.theaircar.com/acf/index.html

So have a duel use motor to drive the Evolt alternator too and let the advance of technology determine which fuel prevails. Of course this adds to the pricing but who knows where oil will go versus the savings potential.

India might be planning to use it, but aren't there too many energy losses or inefficiencies when using compressed air?

Here is the link to the Air Car thread on the old forum:

http://www.gm-volt.com/volt-discussion/?forum=4&topic=261&page=1

Could be interesting for some applications. Personally, I like the idea. My concerns are basically range and how to deal with all the water in cold climates. However, For a dense city with warm climate it could be ideal. Very simple an the only oil needed would be for lubrication.

Zero Pollution Motors has licensed the Air Car configuration for the US, with the intention of adding a gasoline powered heating source for the air entering the air motor:

http://zeropollutionmotors.us/