Hydrogen Fuel Debate: Liquid or Compressed Gas Storage

One of the biggest stumbling blocks to making hydrogen-powered vehicles a viable form of personal transportation is the building of distribution infrastructure. BMW's Hydrogen 7 sedan, powered by a liquid hydrogen burning internal combustion engine, has been tooling around major cities across the world for the last two years, and that's exactly the problem. Major cities are among the only places that have liquid hydrogen fueling stations. Why, what's the problem?

A large part of it is the ongoing debate over whether fueling stations should carry liquid or compressed gas hydrogen. BMW is committed to hydrogen combustion as the solution to zero emissions vehicles and prefers the use of chilled (cryogenic) liquid hydrogen which has a much denser energy storage capacity. The downside is a slow loss of volume over time, through parasitic warming. Currently, simpler (though less energy dense) compressed gas hydrogen storage is the predominant technology for fuel cell powered vehicles (among them the Honda Clarity, Chevrolet Equinox FCEV and Toyota FCHV) which chemically convert hydrogen to electricity rather than burning it. For obvious reasons, distributors want the debate settled before committing resources to building a network of fueling facilities.

To stay in the game, and hopefully end the impasse, BMW has been been working on a different form of storage--Cryo-compression. This approach uses a conventional compressed gas storage tank that is chilled (and insulated) to increase its volume (energy density). Though it's still in its infancy, this design would also allow the storage system to accept both gaseous or liquefied hydrogen.

This is a great idea, and we're interested to see how it all pans out. Let the games begin.

BMW Hydrogen 7 refueling - photo © BMW