Fuel cells, which were first conceived in the 19th century, can create power by putting a gas -- such as hydrogen or methane -- in contact with a reactant, in the presence of a catalyst. Fuel cells are low in pollution, very reliable and generally more efficient than competing technologies, but the manufacturing plants are expensive to build. According to the latest data available from Price WaterhouseCoopers, shipments of fuel cell systems in 2009 were approximately 24,000 units, an increase of 41 percent over 2008. FuelCell Energy is no newcomer to the technology, having been founded in 1969 in Danbury, Conn. It shipped its first commercial power unit to the Kirin brewery in Japan in 2003. Now its power generators can be found throughout the world in a diverse range of industries -- from an onion farm to a bakery that uses organic waste as fuel, to a California prison. In fact, many of its commercial sales have gone to California, the leader in America's push for green energy. That said, South Korea remains FuelCell's largest market.