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.

Cool Idea, Very Cool

The BMW Hydrogen 7 runs on liquid hydrogen, not gaseous hydrogen. There are only about 50 hydrogen fueling stations in the United States, and just a handful of those dispense liquid hydrogen. Even if you happen to have access to liquid hydrogen station, you’ll still face a number of other drawbacks and obstacles. First, the BMW Hydrogen 7 has a zero-to-60 time of almost 10 seconds, which is about 45 percent slower than a conventional 7 Series with a V-12. Trunk space has been cut in half to make way for the bulky hydrogen fuel tank.

Speaking of the tank, it’s more accurate to think of it as a giant thermos, because the temperature of hydrogen must drop down to about 400 degrees below zero Fahrenheit before reaching a liquid state. If that chilly temperature is not maintained, then you face the problem known as “boil off,” a process which is difficult to avoid. When the car is not in use—for as little as one day—the liquid hydrogen begins boiling off. Half the fuel is gone in eight days time. Therefore, this car is actually more efficient on the road than in parked in a garage.

For now, the problems of the Hydrogen 7 belong to very short list of people. BMW has leased a limited number to high-profile individuals interested in touting the green attributes of hydrogen fuel.