BMW Hydrogen 7 Prototype

• Looks like: BMW 7 Series
• Defining characteristics: Burns gas or hydrogen gas
• Ridiculous features: Requires liquid hydrogen, which is rarer than hydrogen gas
• Chance of being mass-produced: Up to 100 will be built; 25 percent for U.S.

If you don't sweat the details, it might seem like hydrogen cars are a reality in the U.S. market. The important details are that the fuel-cell cars presently in the hands of consumers are on lease and worth roughly $1 million each, and that the BMW Hydrogen 7 isn't a fuel-cell vehicle. Rather than using hydrogen to generate electricity in a fuel cell, it burns hydrogen gas in its conventional V-12 engine. It also can burn gasoline at the flip of a dashboard switch.

Hydrogen gas burns cleanly, producing only water vapor, which is the claim made for fuel cells, too. That's not really the point here. Neither is cost; burning hydrogen currently costs more than burning traditional gas. The point behind burning hydrogen in an engine is to give energy and distribution companies another incentive to provide hydrogen. The circle is vicious: Automakers don't want to build cars for which there's little fuel, and fuel companies don't want to provide a fuel that no one will use. Another use for hydrogen gas can only help build the infrastructure for our inevitable switch to fuel-cell/electric power.

Makes sense? It does until you find out that the Hydrogen 7 — a 7 Series sedan equipped with two tanks and two fuel systems — needs to be filled with liquid, not gaseous, hydrogen, which is even rarer. There are 31 hydrogen gas stations in the country, 23 of which are in California. Only a few dispense liquid hydrogen, but they all receive and store their hydrogen in liquid form. BMW says it's hoping to convince these outlets to dispense liquid hydrogen, too.

A pressurized hydrogen gas tank wouldn't give a car enough range. The Hydrogen 7's 125-mile range relies on liquid that's converted to gas for burning. A full gasoline tank adds 300 miles for a total of more than 400 miles at cruising speeds. BMW says the acceleration is the same whether the car is running on hydrogen or gasoline. That said, the zero to 60 mph time is more than 9 seconds — far longer than a conventional 7 Series with a V-8 or V-12 engine.

The other tradeoffs include trunk space, which is cut in half to accommodate the hydrogen tank, and the odd nature of liquid hydrogen overall. The liquid form is uncommon because it has to be kept at cryogenic temperatures to prevent its evaporation. Storage facilities require big-time refrigeration. The Hydrogen 7 uses a superinsulated storage tank. Its 1-inch-thick insulation is equivalent to 17 meters of Styrofoam, according to BMW. It could keep coffee hot for three months. Unfortunately, liquid hydrogen's requirements are greater. When the car isn't using the fuel, it builds pressure. When that pressure gets up to 87 psi — after roughly one day unused — it starts to "boil off," to vent harmlessly, mixed with oxygen by a catalytic converter to create water vapor. The problem is that it can boil off half your fuel in eight days.

Compared to fuel-cell cars, the Hydrogen 7 is relatively cheap, but BMW won't be selling it. Like the Honda FCX fuel-cell car, the BMW will be leased, to VIPs of the company's choosing.