Affordable as in under 50,000.
go see the movie Who Killed the Electric Car. Fuel cells are a cynical pie in the sky way to draw attention away from electric cars.
I agree the technology may exist in a decade or so, but it will also depend on the cost-effectiveness (and willingness) of changing from the petroleum-based infrastructure to a hydrogen one.
I don't picture Hydrogen will ever be the most desirable fuel as it's inheirently very explosive. Conceivably Hydrogen could be used to replace AVgas if we go over to corn or pig fuel but I don't imagine it would be used for cars on a widespread application.
Forever. There is no energy-efficient way to make hydrogen. Industrial hydrogen is mostly made from natural gas, but can be made by electrolyzing water in a very energy-intensive process. Not only is hydrogen costly in terms of energy required to make it, it is difficult to handle: it cannot be shipped through the same pipes that are used to transport natural gas, because it invades the grain structure of the steel and weakens it. (It could be transported if you lined all the pipes. But I would not like to rely on a lining remaining leakproof.) To be used in a vehicle, it must be stored either in liquid form -- which requires a lot of energy to make, as liquid hydrogen is the second coldest liquid there is -- or pressurized to exceedingly high pressures -- typically 5000 psi. Thus, special handling would be needed -- your Aunt Hattie isn't going to be able to drive into a service station and fill up her Newmobile with hydrogen. The density of hydrogen is so low that a standard welding cylinder filled with the stuff contains barely more energy than a half gallon of gasoline.
