Fuel Cell

I've been looking at Fuel Cell stuff. I think Direct Methanol Fuel Cells (DMFC) are the most likely candidate for transport-based solutions. They operate in reasonable temperatures and with reasonable humidity. Other fuel cells are much more picky.

I think the basic construction is making a sandwich with the membrane between an anode and a cathode. The membrane needs to be in contact with the methanol mix on one side and air on the other side. You heat the fuel up and the whole thing just goes. It spits out CO2 and H2O (vapour) which are relatively clean.

It seems that a company called PolyFuel make the best membrane for use in a DMFC. They claim 500milliwatts per cm-sq. I calculated this to mean that for a relatively powerful motor of 85kw you need 27m-sq. I guess you could do this with a stack of 5 or 10cm-sq cells in the circuit. Then you just need fuel-delivery and a method to ensure you don't get dirt everywhere.

So, remaining questions are: how fast does the fuel get used up? How much does the membrane cost? What am I missing in terms of construction? How good is an electric motor at converting the electricity to rotational energy? How big a battery will I need to start the thing up?