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Hydrogen can be used as a transportation alternative providing rapid fill up of vehicles and very low pollutant emissions. However, when considering the feasibility of hydrogen it is necessary to ask: where is the hydrogen coming from? and what penalties am I taking in converting my primary energy source to hydrogen? 

Hydrogen is not a naturally occurring gas.  Hydrogen must be processed from either fossil fuels, or electricity.  In general, it is more efficient and cheaper to use the primary energy source directly avoiding intermediate hydrogen conversion all together.  For example when electrolyzing water to form hydrogen for transportation much of the primary energy (in this case electricity) is wasted as heat.  Electrolyzers are 80% efficient at best.  With a 50% efficient fuel cell, it means that if 100 units of electricity are used to generate hydrogen about 40  units of electricity (0.8x0.5x100) will be recovered for transportation at best (more then half is wasted).  On the other hand if electricity was used in battery electric vehicles or direct electric transportation approximately 80 percent of the primary electricity can be used for transportation.  In such scenario over half the electricity is lost in hydrogen conversion steps that can be avoided all together.

To generate hydrogen from natural gas complex reactors must be used to reform methane and for hydrogen cleanup.  The extra-conversion steps from methane to hydrogen will add unnecessary costs with minimal if not negative efficiency benefits.  So why consider hydrogen at all?

The reason to consider hydrogen is because it is carbon free.  One main scenario where hydrogen may be beneficial is coal to hydrogen where the carbon in coal can be captured in sequestered.  In such a case coal cannot be used directly in the vehicle.  Converting coal to hydrogen makes it possible to use coal as a transportation fuel without carbon emissions.  In advanced gasifiers of the future, it will be possible to convert the dirtiest fuel of all- coal to the cleanest fuel of all- hydrogen all with very limited pollution emissions. In such a vision hydrogen pipelines can be used to transport coal plants to cities. 

Storing hydrogen on board the vehicle is often thought as unfeasible and dangerous, due to hydrogen very low volumetric energy density.  However by storing hydrogen at high pressures (e.g. 700 bars) major automobile companies including GM, Toyota and Honda have achieved reasonable vehicle range.  By designing hydrogen cars around hydrogen safety concerns, hydrogen vehicles are considered to be comparable or safer then gasoline vehicles.  Hydrogen is a very feasible transportation alternative.  The question one must ask is: where is the hydrogen coming from and what penalties am I taking in converting my primary energy source to hydrogen?  Hydrogen is an energy carrier and should be evaluated critical for the future of energy.

A hydrogen fuel cell public bus accelerating slowly at traffic lights in Perth, Western Australia (Source:http://en.wikipedia.org/wiki/Image:Hydrogen_fuel_cell_bus.jpg)