A quick walk through the alternative cars on display at the Sacramento Convention Center made it clear that while there is still a lot of interest in "pure" electric vehicles - Toyota now sells a pure electric RAV 4 SUV - the automotive industry is still convinced that cars must be able to generate energy on board. The real star of the EVAA meetings, therefore, was the "hybrid" automobile, in which an electric motor is powered by some form of onboard engine that runs on gasoline or some other liquid or gaseous fuel. Two such cars, Toyota's Prius and Honda's Insight, are already on the market.

That, however, is where the consensus ends. The ways in which a hybrid can be constructed seem almost endless. So, too, the options for fueling the onboard internal combustion engine, with natural gas, methanol, ethanol, and gasoline all having their proponents. And that is only the beginning. Some hybrid vehicles receive most of their power from the electric grid. Others rely on microturbine engines.

The focal point of the Sacramento show, meanwhile, was the fuel cell, which produces electricity by combining hydrogen with oxygen in a chemi-cal reaction. The fuel cell designs were as varied as the hybrid ones; some versions relied on hydrogen stored in liquid form, or as a gas, or in a solid state, or in solution, or even on methanol or natural gas. Indeed, the plethora of alternative fuel cell models was one reason for the vagueness of the Bush administration's plans, announced last May, to subsidize further development of the technology.