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Laboratory tests show that the proton exchange membrane (PEM) fuel cell can be a fast-response power source able to produce full power in less than 200 μs. For every standard cubic foot (28.3 liter) of hydrogen, approximately 45 Whrs of electrical energy can be produced from a PEM fuel cell. A 100 kW PEM fuel cell would weigh approximately 300 lbs (136 kg) at the current level of material technology. S i n c e t h e f u e l c e l l c a n o p e r a t e f o r many years continuously, the duration of power sustainment depends upon the quantity of stored reactants. Using hydrogen and oxygen, a PEM fuel cell results in one of the highest energy density power devices for the UPS application. Hydrogen storage methods discussed include gas, l i q u i d, metal hydride, and carbon a d s o r p t i o n.

Using only 650 lbs of liquid hydrogen, a full size transit bus driven by electric motors can travel non-stop for 3,000 miles. The energy conversion comes from a 150 kW fuel cell at 55-65% efficiency. The two types of fuel cells that will be practical for rubber-wheeled transportation at this time are the proton exchange membrane (PEM) and the alkaline type. Advanced batteries will be incorporated in the design to assist with acceleration and for regenerative braking. The low temperature hydrogen will help to cool the fuel cell, increase power output of the electric motors, and cool the passenger space. The bus will have four independent wheel drives, with 4 -wheel steering to reduce turn-radius. The purpose for this demonstration bus is to lay the design foundation for zero-emission urban buses.

Carbon adsorption has been found to be an excellent method to store hydrogen. This is an ideal method for weight sensitive applications without the high pressures of compressed hydrogen gas, and the cryogenic temperatures of liquid hydrogen (20°K/-253°C). At 150°K (-123°C) and 55-atm (810-psig), hydrogen is adsorbed in its condensed phase over the vast surface area of the carbon. The adsorption method can store nearly 2-times more hydrogen than in pure compression at the same conditions. Hydrogen combustion by-product is solely water. In air, combustion by-products also include a small quantity of Vehicles fitted with hydrogen fuel cells can deliver the same power and twice as much range as gasoline or diesel vehicles, but without the pollutants. Hydrogen is the cleanest and most efficient fuel known, and it is totally renewable.