The fierce debate over the prospects for hydrogen as a clean, renewable energy source for the future has dragged on for decades. The pro-hydrogen forces periodically trumpet important breakthroughs, only to be knocked back by disappointing setbacks. It seems that hydrogen's real-world feasibility has been "just around the corner" since the 1970s. Hydrogen advocates have long touted the invisible gas as an abundant, potent, storable, non-polluting form of chemical energy - and it is indeed all of these. Hydrogen is the most common element in the universe. Every nation can produce it and hydrogen will never run out. One of its unflagging champions is Peter Hoffmann, the German-American editor and publisher, who has weighed in on behalf of hydrogen for years and his revised classic, Tomorrow's Energy, brings us right up to date with scientific and commercial developments, as well as the often turbulent political discussion. His argument is that hydrogen technology, in the form of fuel cells, is, well, just around the corner; all that's needed is for policymakers to wake up, dig a bit deeper in their pockets to provide more R&D funding, and start laying an infrastructure for fuel cell-powered mobility. This will be the beginning of the age of hydrogen, which has the potential, eventually, to consign the hydrocarbon economy to the dustbin of history. This bigger goal, though, is a long way down the road in the estimation of almost everyone. The facts about hydrogen, at least, are undisputed: it does not exist freely in nature; most hydrogen is bonded to oxygen in water. It must be generated by splitting it from a compound like water or hydrocarbons like natural gas, oil, coal or plant sugars. Thus, hydrogen is not a primary energy source, like oil, but more of an energy carrier, like electricity. It requires another primary energy source to produce it, which could be renewable, nuclear or fossil. It stores energy that is released cleanly when it is discharged "like the spring in a mousetrap", noted one observer. Hydrogen takes different forms - gas, liquid, or even solid - and is a staple in many industries for the production of fertilisers, drugs and plastics. It converts heavy petroleum into lighter forms suitable for use as fuels. Hydrogen has several potential roles as the fuel of the future. It can be burnt in modified internal combustion engines - like those of jets, turbines, four-strokes and diesels. Over the years, considerable R&D has been expended on this option, but it has never been ready for prime time. Its success is ultimately the key to the "hydrogen economy" utopia that is dreamed of by such renowned voices as Jeremy Rifkin, the US economist and social thinker. The best bet these days are hydrogen fuel cells, which can be used in motor vehicles to store and create electricity. These cells are little electrochemical factories that combine hydrogen and oxygen in a flameless process that produces electricity. Today most hydrogen is generated with fossil fuels, thus making it a fellow contributor to global warming. But this process can also be clean and green if based on renewables, and thus could power future generations of electric cars and the only emission coming out of an exhaust pipe would be innocuous, run-of-the-mill steam. Among hydrogen enthusiasts, fuel cells are the embryo of the hydrogen economy. Fuel cells, argues Hoffmann, "have become widely recognised as a vanguard technology that may launch hydrogen energy on its way to becoming a major environmentally benign, sustainable, renewable component of the world's energy mix for both transportation and stationary applications". By "stationary applications" he means heating homes.