Pyroelectric energy harvesting,

   Electrostatic (capacitive) energy harvesting,

   Blood sugar energy harvesting, and

   Tree metabolic energy harvesting.


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. Fueled systems derive oxygen for combustion from the air arrangement that has both good and bad features. First, the mass of the oxygen used in the energy production process is not carried by the Soldier and second, the energy content of the fuels is large compared to that of batteries, which both store and deliver energy. On the downside, the fuel’s need to ingest air for combustion in turn necessitates the ability to shut the fueled system off when there is a potential for clogging or contaminating the unit. Doing so renders the fueled system unusable until it can “inhale” clean air again. To mitigate these problems, fueled source-rechargeable battery hybrids are being researched, and a few have been introduced on a limited basis to the Soldier. The state of the art for hybrid systems is depicted in Table I-5. The data assume a 72-hr mission.

TABLE I-5. State of the art in hybrid systems

Power Train Weight (lb/kg) Volume (in3/cm3) Energy (Whr) Average Power Capability (W) Specific Energy (Whr/kg) Comments
Six Li-145 batteries (all- battery baseline) 13.2/6.0 216/3,540 870 12.0 145 Inventory
4G Zn-air fuel cell/Li-145 battery 9.4/4.3 218/3,572 1,145 16.0 266 Inventory
Methanol fuel cell/Li- 145 battery 6.1/2.8 94/1,540 895 12.4 319 Experimental limited rate initial production

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