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.