Review of Autonomous Undersea Vehicle (AUV) Developments 
ELECTRIC POWER SYSTEMS 
The NSB also assigned one panel to focus on those electric power generation, storage, and 
propulsion technologies that, when applied as a system, will support the electrification of ships, 
submarines, and land-based vehicles [2]. It surveyed the status of key elements of power 
systems such as energy storage devices, electric power recovery subsystems, and battery 
technologies. Industrial development is ongoing in most of these areas, and current trends 
suggest steady improvement in capacity, density, modularity, and reliability. The Naval forces 
can take advantage of commercial developments by actively monitoring the commercial marine 
power and propulsion sector and by applying a top-down systems engineering process to fleet 
capability upgrades. Of the technology areas covered by the panel, fuel cells and batteries are 
covered in this report since they hold the most promise for AUV applications. 
Fuel Cell Power Systems 
The panel had the following comments regarding fuel cell power generation technology [2]. 
(Table 1 lists the available fuel cell systems.) 
"Fuel cells hold promise for zonal power generation. They are a particularly efficient and clean method of 
utilizing hydrocarbon fuels and are appropriate for medium-sized power generation units (1 to 4 kW). 
Hydrogen-based fuel cells electrochemically oxidize hydrogen with oxygen (or air) and directly convert 
chemical energy to electric energy. The product of this combustion is water, and this combined with the 
extremely low signature of the cell make it a very attractive power alternative for Navy and Marine 
operations. Because they are essentially isothermal devices and therefore not limited by heat engine 
thermodynamics, they can in principle have very high energy densities (watthours per kilogram), limited 
only by the specific free energy change in converting hydrogen and oxygen to water. The great obstacle to 
hydrogen-based fuel cells for mobile, battle-zone applications is the volumetric problem of storing 
hydrogen. Although hydrogen produces a great deal of energy on a weight basis, it produces very little 
energy on a volume basis, even when stored at high pressure. 
Today hydrogen is the only fuel that can be electrochemically oxidized in a fuel cell system at practical 
rates. The ideal system would directly convert the free energy of combustion of other fuels, such as 
hydrocarbons, into electric energy. Other fuels are used in prototype fuel cell systems by either externally 
or internally reforming them to a mixture of hydrogen and carbon dioxide, then using the hydrogen 
electrochemically in the fuel cell. A major breakthrough in electrocatalysis would be required before other 
fuels could be electrochemically oxidized at useful rates. 
Hydrogen fuel cells are impractical for at-sea applications because of the space required to store hydrogen, 
but hydrocarbon fuel conversion designs would be directly applicable to Navy use. Most units under 
development (primarily in the automotive industry) require higher-quality fuels than standard Navy 
distillates. Although there is no current evidence of an impending technical breakthrough in this area, the 
promise is such that near-term programs to develop converters for standard Navy fuels should be 
encouraged. 
Fuel cells convert chemical energy directly into electrical energy and as a power generation module can be 
viewed as a continuously fueled battery. They take in fuel and oxidant and produce electricity, water, and 
heat. In addition to the fuel cell stacks, the power generation module includes heat exchangers, regulators, 
controls, and fuel-processing and other auxiliary equipment. Besides enhanced energy density and 
efficiency, fuel cells have the potential for providing power with little or no emission of regulated pollutants. 
Other attributes include low-noise, reduced-exhaust IR signature, improved reliability and maintainability, 
and a high degree of modularity. Table 1 provides a summary of characteristics for the alternative fuel cell 
technologies being considered. It is anticipated that when fully matured, fuel cell costs could be as low as 
$500/kW. 
Most of the fuel cell development to date has been focused on electric utility applications that use natural 
gas for fuel and for which compactness is not required. Recent developments include transportation 
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