The calculations for Figure C-5 are made with a simple equation, given below for a 2,000-Wh/kg system with a 1,440-Wh mission on methanol (6,088 Wh/kg):

A similar equation is used to generate the data plotted in Figure C-5 for a 2-kg dry system:

The plots in Figures C-4 and C-5 show that for a 20-W system used for 72 hr (1,440 Wh), a greater dry system mass can be tolerated by a fuel cell or engine that operates on JP-8 rather than methanol. A 30 percent efficient DMFC must weigh 1.6 kg to operate at 600 Wh/kg, but a SOFC running on JP-8 can weigh 2 kg. This discrepancy is simply due to the energy content of the fuels. One can infer from the plots that system efficiency and system weight are the key factors affecting the specific energy of the system. Also, systems with efficiencies below 10 percent are limited in their specific energy—for instance, a 1,000-Wh/kg system can never be achieved by a methanol-fueled system with 10 percent efficiency (Figure C-5)

The equations can be used to estimate the viability of certain systems for various missions. For a 480-Wh mission (20 W for 24 hr), any JP-8 fueled system with a target specific energy of 1,000 Wh/kg would have to weigh less than 400 g; the task of integrating the device, the insulation, the fuel tank, and so forth would be a challenging one. However, when the mission duration is extended to 4,800 Wh (10 days at 20 W), the fueled systems become highly attractive.

Cairns, Elton J. 2004. Battery overview. Chapter B. Encyclopedia of Energy, Vol. 1. C.J. Cleveland, ed. New York: Elsevier, 124.

Chase, M.W. 1986. JANAF Thermochemical Tables, 3rd ed., vols. 1 and 2. American Chemical Society.

NRC (National Research Council). 2003. Science and Technology for Army Homeland Security: Report 1 . Washington, D.C.: The National Academies Press.

Panasonic. 2003. Panasonic Nickel Metal Hydride Handbook. Available at http://www.panasonic.com/industrial/battery/oem/chem/nicmet/index.html. Last accessed on December 23, 2003.

Front Matter (R1-R22)

Executive Summary (1-8)

1 Introduction (9-13)

2 Technology Alternatives (14-26)

3 Power System Design (27-36)

4 Soldier Energy Sinks (37-45)

5 Progress (46-55)

6 Future Warrior Design Concepts (56-65)

7 Recommendations (66-71)

References (72-72)

Appendix A: Biographical Sketches of Committee Members (73-77)

Appendix B: Committee Meetings and Other Activities (78-79)

Appendix C: Measures of Performance (80-87)

Appendix D: Source Technologies (88-114)