Batteries are the generic solution for soldier power. They will be an integral part of hybrid and stand-alone energy sources for the foreseeable future. The challenge is to make them smaller, lighter, cheaper, more reliable, and more energy-dense without sacrificing safety. Fuel cells are the focus of intense interest by the military because of their potential as instantly “rechargeable” energy sources that can meet specific energy requirements for high electrical loads and long mission lengths. Like metal/air batteries, fuel cells are air-breathing devices that cannot operate when submerged in water. Future acceptance of fuel cells on the battlefield will be determined to a great degree by logistics, because current prototypes are fueled by the nonstandard logistics fuels (methanol and hydrogen).

Recommendation 1: The Army should focus on batteries with a specific energy of 300 Wh/kg and higher for insertion into future versions of the Land Warrior (LW) ensemble. It should continue to promote and support innovative approaches to disposable and rechargeable batteries that can be adapted for military use. To select the best candidates for a given application, the Army should explore the trade-off space that exists between lifetime (measured in terms of charge-discharge cycles), specific power, specific energy, safety, and cost.

Batteries currently add a substantial burden to the heavy load carried by the dismounted soldier. Use of disposable batteries in training and field operations has proven to be a substantial expense. Employment of rechargeable batteries for many applications promises to reduce life cycle cost but adds the cost of additional equipment and the logistics complexity of recharging in forward areas. Fueled hybrid solutions offer even greater promise than rechargeable batteries in reducing weight for longer missions. These have operational advantages and limitations but add tasks for the logistician, who would have to deal with another nonstandard fuel to be carried forward.

Recommendation 2: The Army should evaluate the applicability of small-scale, portable fuel processors capable of reforming the Army-standard fuels for use in proton exchange membrane (PEM) fuel cells or solid oxide fuel cells (SOFC). Scaling laws should be determined and cost/benefit analyses should be performed to determine whether there are power levels and/or mission durations that make such reformers an attractive alternative.

The Army must determine whether an alternative, nonstandard fuel source (such as methanol, hydrogen, or ammonia) is logistically acceptable. A proper analysis of trade-offs would permit decision makers to make an informed judgment on whether the operational advantages outweigh added logistics complexity and costs. Ideally, this would include testing in line units (even if only at the squad level) under representative field conditions. It would also save the Army money otherwise invested in research on fueled system alternatives that do not make logistical or operational sense.

Recommendation 3: The Army should immediately conduct a comprehensive and definitive analysis of the operational and logistical implications of fielding nonbattery solutions as power sources for dismounted soldiers. This should include consideration of operational benefits, logistical limitations, and life-cycle costs, as well as considerations of safety and risk. It should develop models of competing energy sources, including fuel cell systems, and use them in simulations of battlefield operations. The data can then be combined with estimates of system costs to conduct cost/benefit analyses that would either support the consideration of non-standard-fueled fuel cell systems or eliminate them from consideration.

Several internal and external combustion engine prototypes have been demonstrated and show potential for military applications. Microturbines have not to date demonstrated the ability to provide a net positive system power output. Stirling engines use standard logistics fuel (JP-8) and could serve as a power source for battery rechargers or to meet anticipated requirements for high-demand microclimate cooling and exoskeletal applications. All small internal combustion engine systems now available have distinctive acoustic and heat signatures that would restrict their utility in combat. Stirling engines are inherently quiet but have significant thermal signatures.

Recommendation 4: The Army should adjust the focus of internal combustion engine development to demonstrate net power outputs and balance-of-plant systems appropriate to specific Army applications. Heavy emphasis should be placed on developing packaged systems with reduced heat and noise signatures. Once power output capabilities are demonstrated, the development should focus on improving system efficiencies.

Hybrids offer enormous advantages from a simple energetics point of view for longer mission times. A hybrid power/energy system can be optimized for both high energy and high power demands. It can also provide the means to overcome the disadvantage of an air-breathing power source