The launch of an affordable hydrogen-powered car is a major milestone. But fuel needs to flow in order to run it. Right now, that's a problem. In some markets around the country, hydrogen gas is available via pipeline, where it's used in industrial and commercial settings. Elsewhere, it must be stored at filling stations in large pressurized tanks. So far, there are only 12 such stations in the U.S., and 10 of them are in California. Over the next five years, the state is investing $200 million and partnering with several gas providers and automakers to open 100 more. Similarly, the Department of Energy is working to expand stations nationally. Even so, hydrogen still faces a fundamental economic hurdle: Refining the gas uses a lot of energy, which makes hydrogen cars less efficient than their battery-electric and gasoline-powered peers—at least until cleaner production methods come on line.