As we envision the hydrogen age today, it will rely heavily on fuel cells to power our homes and cars. What is a fuel cell? In a simple sense, it's a device that chemically produces electricity from an added fuel. Standard batteries make electricity too, but their ingredients are sealed inside and eventually run down. When the fuel gets low in a fuel cell, you just add more.

Fuel cells are small and quiet. The unit in your car, for instance, might be a box hardly bigger than a case of beer. Technically, the box would contain not just one big fuel cell but many small ones that together power the car's electric motor. You'd fill the car's tank with hydrogen, which then would be converted cleanly into electrical power in the fuel cell without releasing any pollutants.

Some businesses see fuel cells as a way to protect themselves against the costly computer crashes triggered by power failures. It's another factor pushing us toward something more decentralized and weblike than our present energy system.