Hydrogen Cars

Hydrogen fuel cells sound to some like a promising technology: it allows an electric car which can be refueled quickly and its only emissions are water.  But it's up against some laws of physics that make it tough to be practical.  The main one is that the energy density of hydrogen is very low.  Liquid hydrogen has an energy density 1/4th that of gasoline.  This means to get a car with the same range, you'd need a gas tank 4 times as large.  But liquid hydrogen is incredibly expensive and the tank would be impractical.  Carrying it at much higher than about 3000 PSI (roughly what is used in a SCUBA airtank) is probably impractical, but at that pressure, the energy density is about 1/20th that of gasoline.  To replace the the 11.9 gallon fuel tank and internal combustion engine in a Prius with fuel cell and a 3000 PSI hydrogen tank and get the same range would take a tank of around 250 gallons.  This is a volume of about 33 cubic feet.  This is roughly the entire interior volume of the Prius....if you take out all the seats!

The bottom line here is that without some significant technological breakthrough (for example extremely high pressure tanks, or some scheme that where the hydrogen is dissolved in some other material at much higher than 3000 PSI equivalent), a hydrogen car isn't likely to have much range.   A bus or truck is a different story: it has a lot more places to put the tank(s).   Hydrogen does have one big advantage over gasoline or battery electric: the mechanism, tank, fuel (even 250 gallons), fuel cell and electric motor, is a lot lighter.  This may help with mileage to some extent but nothing like enough to give it the range we've come to expect.

Nevertheless, Toyota has just announced the Toyota FCV, a Camry-sized Hydrogen fuel cell car to be put on the market in 2015, which they claim has a 300 mile range and can be refueled in 3 minutes.   I'm skeptical.   None of the pictures show the interior or even say how many passengers it carries.  It pretty much has to be a bunch of hydrogen tanks on wheels, with very little room for the occupants.


In most places the cheapest way to make hydrogen involves heating natural gas with steam to split the hydrogen from the CO2.  This produces as much CO2 as burning it (even more if you burned something to produce the steam) and is at least as bad for the CO2 levels in the air as other fossil fuels.  It is NOT a green fuel, it is a fossil fuel, with all the problems that come from it.  The CO2 isn't coming out of the tailpipe of the car, but just as much (more actually) is coming out of the plant.

In some places, where you have extremely cheap electricity, you can make hydrogen with electrolysis of water. It takes more energy to do this than you will get out of it, so it makes the hydrogen a sort of storage battery, but because of the ease of refueling and the light weight may give it an advantage.  Iceland, with abundant geothermal electricity, is such a place, and as the whole island is only 250 miles across, a low range car is pretty practical.

Hydrogen is no more flammable than gasoline, although if punctured, a high pressure tank would spray a stream of hydrogen until it's exhausted.  If it ignites, that's potentially a very hot, very focused flame.