An Extremely Compact Uninteruptible Power Supply Based On Fuel Cells

Critical systems need protection from power failure in the field environment. The current generation of uninteruptible power supplies (UPS) is based on storage batteries. This severely limits power density and causes the size of the unit to rise rapidly as the discharge time required increases, since most of the weight and size comes with the batteries. Replacing the storage batteries with a system consisting of a fuel cell, electrolyzer, and gas storage allows a significant increase in the power density and a concomitant decrease in the size of the system. In this system, while power is available, the electrolyzer converts water into hydrogen and oxygen for storage. When the power fails, the fuel cell, which is kept fully charged with gas and waiting at its full open circuit voltage, recombines the hydrogen and oxygen to produce electricity. Since only a small portion of the system, the gas storage, is devoted to energy storage the rate of increase in size with increasing discharge time is reduced. Using fuel cells instead of batteries keeps all of the desirable features of batteries (rapid start-up, ambient temperature operation, and electrical recharging) while substantially reducing system size and weight.