"We definitely feel like we are driving a prototype vehicle, but for the most part it drives pretty well,'' said Konkle, who has driven earlier versions of fuel-cell cars that had scant power.

But that doesn't mean pollution-free cars running on the most plentiful element in the universe are around the corner. In fact, the city's loaner from Ford Motor Co. is proof of the challenges to fuel-cell powered vehicles.

The byproduct of using hydrogen - water - becomes a solid at a much higher temperature than gasoline, which means the car has been in storage over the winter. And there's the problem of how to squeeze enough hydrogen into a tank on a car to give it the same range as current vehicles.

Officials at Ford say it will be 10 to 15 years before a commercial version is viable. General Motors Corp. has a more ambitious timetable, but a top University of Michigan fuel researcher says the hydrogen cars are a long way off.

Jerry Mader, the energy research director at the University of Michigan's College of Engineering, thinks it may have been a mistake to roll out test programs like the one in Ann Arbor. He thinks it will be closer to 2020 or later until it's a viable technology.

The U.S. Department of Energy, at the urging of the Bush administration, helped fund the program that puts automaker's fuel-cell vehicles in the hands of municipalities for a two-year test. Valuable data can be obtained, but Mader fears the program could backfire.

"I really feel like this was a move by the Department of Energy to get more support for the program, sort of a marketing tool,'' Mader said. "If the technology is too immature, it can have the opposite effect. It's not that it's no good, it's not ready yet to be introduced.''

That's not to say Mader isn't interested in fuel-cell technology. In fact, he thinks the move away from oil dependence is the single most important issue facing the United States. Instead, he worries that promising too much now may sour people on the technology and lead to less funding.

While automakers are working with several kinds of alternative energies, they agree that fuel-cell cars are the key to addressing the problem of dependence on oil.

Hybrids and diesels don't address that central problem, said Scott Fosgard, GM's spokesman over new technologies including fuel cells.

"As great as hybrids are, they can't keep pace with the growth,'' he said. "The only other technology I'm aware of that can also get you on that pathway is hydrogen.''

Fuel-cell obstacles

Ford is just now returning the fuel-cell car after holding it for six months. Ann Arbor officials drove it around for about a month last fall before it had to go back. It will be on display at an Earth Day event on Saturday at the University of Michigan Matthaei Botanical Gardens.

"This whole idea that the byproduct is water and not pollution is very interesting, but of course it's water that is causing these problems,'' Konkle said.

Figuring out a way to keep hydrogen-powered cars running during the half of the year in Michigan where temperatures fall below freezing is a pretty big obstacle, but it's not the only one, and it might be the easiest to solve.

In fact, GM and Honda have already been able to build fuel cells that work in sub-freezing temperatures, at least in the short term.

Current fuel cells need almost pure hydrogen, which is difficult to produce. The easiest way to get it is to break down natural gas but cars already can - and do - run on natural gas, and it is following oil's price trajectory.

The materials to make fuel cells are costly, there's a lack of infrastructure in place to create and transport hydrogen, which likely would have to be liquefied through a super-cooling process. And keeping it that cold would take lots of energy, defeating the purpose of using hydrogen in the first place.

The ideal way to get hydrogen is from water, but that requires a lot of energy, and then it has to be stored somewhere and transported, Mader said.

His group is working on projects where hydrogen is created as a byproduct of nuclear power production. The plants create huge amounts of heat that require cooling with water anyway. Hydrogen could be created under those conditions.

And no one has been able to tackle the hydrogen storage problem easily.

The 200-mile range on the Focus that Ann Arbor has comes with a price. The tank takes up the entire trunk.

Nick Twork, a spokesman for Ford, said that even making fuel-cell vehicles commercially viable wouldn't mean that the companies would start making them.

In fact, Ford is aggressively pushing gas-electric hybrids, flexible gas and ethanol engine, clean diesels and even hydrogen-fueled internal combustion engines.

"The point is, there is no one good solution here,'' he said. "There are so many different variables involved in all of these technologies.''

GM unfazed

General Motors built the first fuel-cell powered car in the early 1960s and the automaker intends to stay in the lead.

GM is strongly pushing ethanol and hydrogen, making smaller efforts in the hybrid engines and diesels.

Fosgard said company officials have given the fuel-cell group a 2010 deadline to design a fuel-cell powered car that would cost the same to produce, and have the same durability as an internal combustion engine car assuming the company produced 500,000 of them.

Fosgard said he is confident the company will be able to do it.

"Does that mean we will be building 500,000 vehicles by 2010? No,'' he said.

But he said obstacles are not as high Mader says.

Fosgard said GM envisions burgeoning markets in Southern California and New York. A study by Royal Dutch Shell Co. and GM showed that it would take 300 hydrogen filling stations to meet the needs of 200,000 drivers in Southern California.

GM has 13 fuel-cell vehicles in real-world driving conditions worldwide, including six minivans in Washington, Fosgard said.

With "200,000 fuel-cell vehicles, then economics would take over and companies would have the volume they would need,'' he said.