Hydrogen fuel-cell: Honda FCX Clarity

For a nearly a generation, hydrogen fuel-cell vehicles have been championed as the long-term solution to auto emissions. Vehicles like the Honda FCX Clarity and the Chevrolet Equinox have brought that dream a little bit closer to reality. But the BMW Hydrogen 7 steers through the hydrogen highway in a different direction—because it isn’t a fuel-cell vehicle at all.

Instead of using hydrogen to generate electricity in a fuel cell, the BMW Hydrogen 7— essentially a 7 Series sedan—burns hydrogen in its conventional V-12 engine. And it can switch to straight gasoline at the driver’s whim. Think of it as a dual-fuel gasoline-hydrogen hybrid. A full tank of liquid hydrogen will grant a vehicle range of more than 125 miles. Add a full tank of gasoline for another 300 miles of interstate driving. Put those two together and the BMW Hydrogen 7 can drive about 450 miles on a full supply of fuel.

Whether using an engine or fuel cell, burning hydrogen produces only water vapor at the tailpipe. But the Hydrogen 7 faces a number of obstacles that fuel-cell vehicles—already challenged enough—don’t have to consider.