Making the Soldier Decisive on Future Battlefields (2013) / Chapter Skim
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Appendix -- IEnergy Technologies and Applications for the Soldier
Appendix -- IEnergy Technologies and Applications for the Soldier
Pages 207-226
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Figure I-1 shows common energy sources in terms of both specific energy and energy density. Specific Energy (MJ/Kg)
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400 half battery Rechargeable possible at TRL 4 The Communications-Electronics Research, Development, and Engineering Center (CERDEC) , the Natick Soldier Research, Development, and Engineering Center and the Army Research Laboratory have research and development programs to overcome current shortcomings of energy sources for the Soldier.
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In the near term, the specific energy and energy density of these batteries are still far removed from what is theoretically possible. The wide disparity between what is theoretically possible for batteries based on lithium chemistry and what is practical shows that there is much room for improvement.
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In its Appendix D, the NRC study Meeting the Energy Needs of Future Warriors, provides a comprehensive comparison of the basic technologies and performance parameters for relevant fuel cell technologies (NRC, 2004)
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This is due to the high internal temperatures that allow fuel oxidation at the anode and largely negate the need for catalyst. The electrolyte in a solid oxide fuel cell is a hard, nonporous ceramic compound that allows versatility in stack construction.
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TABLE I-2. Fuel Cell State of the Art Dry System Power Specific Start up Mass for a Type and Fuel level Efficiency power time 72-hr mission Dry Weight (Watts)
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fuel reforming capability that could be integrated into these fuel cells. Note that both liquid propane and JP fuels have approximately the same specific energy but that liquid propane has about half the energy density in Whr/liter that JP has.
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As an alternative to fuel cells, CERDEC funded research on two types of systems that could use standard battlefield fuels -- small external combustion Stirling energy systems and small internal combustion engine converter systems. External Combustion -- Stirling External combustion engines such as steam engines and Stirling cycle engines have been in use since about 1800 but seem, except in a few embodiments, to have mostly been relegated to history, because internal combustion engines and electrical power from an ever-expanding grid were more efficient.
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Operates on the move. Small Internal Combustion Engines Soldiers in Iraq and Afghanistan purchased commercial Honda generators in the 1-3 kW range to augment their energy sources.
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This device is essentially the first stage of a conventional reformer and the basic physics is understood. The hydrogen in the gas stream should aid starting; the smaller molecules should limit coking; and the technology will build on previous successful efforts for Honda.
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HARVESTED ENERGY There are many small-scale energy conversion technologies that might form the basis for energy harvesting, but they generally cannot be scaled up to industrial size. Several technologies can be applied to harvesting: Piezoelectric materials generate a small voltage whenever they are mechanically deformed.
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While these factors are limiting, the energy is there for the taking, has minimal exploitable signature, and, in current embodiments, is robust, flexible and lightweight. Theoretical efficiencies can be calculated as a function of the material energy band gap and the junction type for exposure to the solar spectrum.
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Figure I-2 shows a deployable portable solar array. Near-Term Solar Solutions Since the solar flux is fixed, improvements in energy conversion efficiency is the only way to increase the energy available to be harvested.
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Biomechanical Energy Biomechanical energy is harvested by a mechanism that can extract energy from the motion of legs, arms, and other body types to drive a generator that converts some of the kinetic energy into usable electrical energy. For the most part, biomechanical energy harvesting has concentrated on leg motion since legs are used repetitively and repeatedly for locomotion, whereas arm motion is highly variable, and arms often do not move substantially when they are involved in load carrying.
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External power input: 8 V to 24 V: Solar, vehicle, fuel cell. Operational speed: 0.5 to 3 m/s (slow walk to fast jog)
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SOURCE: LTC Joseph Hitt, et al., Program Manager, DARPA, "Dismounted Soldier Biomechanical Power Regeneration," presented at the Proceedings of the 27th Army Science Conference, Orlando, Fla., November 29 – December 2, 2010. The mechanics of the Soldier Power Regeneration Kit (SPaRK)
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The authors conclude that the results provide confidence that biomechanical energy harvesting may be a viable "augmentative and emergency power supply for the future network-centric dismounted Soldier."4 TABLE I-4. Energy and Weight of Biomechanical Prototype.
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HYBRID ENERGY TECHNOLOGY Hybrid systems consist of a primary high-energy-density element, an intermediate rechargeable energy storage unit usually capable of higher specific power, and an energy management system that allows the unit to interface with any load. In most embodiments, the high-energy-density element is a fueled system.
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(Whr/kg) Comments Li-air fuel cell NA NA NA NA NA Concept Li-145 battery 225
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2008. Theoretical Energy Density of Li-Air Batteries.
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