What is often considered the Holy Grail of the automotive world — the ability to power vehicles on zero-emission hydrogen — may be closer than we think. Department of Energy Secretary Samuel Bodman, in remarks to the press Wednesday at CERA Week, predicted hydrogen-powered cars and trucks could will be on the market within five years. He said automakers have made “good progress” in bringing down the costs of fuel cells for mainstream applications. But there are still issues with how to safely store enough hydrogen onboard a vehicle to permit long-range driving, he said. General Motors Corp. has been on the leading edge in developing hydrogen-powered vehicles, but even the automaker has had to back off early predictions that the vehicles would be commercially available on a wide scale by 2010. At this point, GM and other automakers are still testing hydrogen technologies in commercial vehicle fleets and in the lab. Meanwhile, they have been promoting ethanol-powered cars and trucks, gas-electric hybrids and cleaner-burning diesels as part of a broad effort to improve fuel economy and address environmental concerns.