Primary battery (includes metal/air)

Mature.

Up to 800 Wh/kg in low-specific-power configurations

Mature.

SOA not significantly advanced beyond NRC (1997) report.

Energy density.

Safety.

Power density.

Environmental impact.

Known

Heavy, one-time use.

Current battery of choice for combat missions.

Potential for use in hybrids.

Secondary battery

Mature.

Li ion: 100 Wh/kg in development.

Mature in commercial applications.

Li ion: 140 Wh/kg available; 200 Wh/kg in development.

Energy density.

Cycle life.

Power density.

Safety and cost.

Known

Stand-alone energy supply for many missions.

Can be used in hybrid mode for high-energy missions.

Fuel cell (hydrogen)

Exploratory development.

Many systems at laboratory scale.

Power levels to 150 W considered.

Beta prototypes with various hydrogen sources tested in field.

Power to 150 W.

Fuel reformers.

Water management.

Safety.

Known

New capability; potential for use in hybrid system.

Less weight.

Cost savings.

Requires new battlefield fuel.

Fuel cell (methanol)

Emerging.

Not considered.

Beta prototypes developed at power levels of 20 to 50 W.

20% efficiency.

Fuel and fuel crossover.

Catalyst.

Cost.

Known

New capability.

Less weight.

Cost savings.

Requires new battlefield fuel.

Fuel cell (solid oxide)

Emerging.

Not considered.

Emphasis on small sizes.

Laboratory prototypes in 20-W range.

Research in high-capacity designs.

High temperature.

Materials.

Integration and systems.

Known

New capability.

Less weight.

Easier to utilize battlefield fuels.

More efficient.

Internal combustion

Some versions mature.

Hobby application sizes coupled to generators.

No commercial products on market.

Commercial applications with motor-alternator combinations in 30 to 100 W/kg range.

Efficiencies greater than 20%in 500-W sizes.

Emerging modified hobby engines operate on diesel.

Fuels.

Vibrations.

Life.

Known

Inexpensive technology.

Potential for high-energy missions.

Can probably be made to function with JP fuels.

Current role as battery charger.

External combustion (includes Stirling)

Not considered.

100 W/kg specific power demonstrated for motor-alternator with efficiency of 29%.

System efficiencies projected to be >20%.

Laboratory 35-to 50-W systems available for beta prototypes; 1- to 2-kW beta prototypes available with ~20% system efficiencies.

System-specific power appears to be around 30 W/kg.

Fuels.

Specific power.

System-specific energy.

Signatures.

Known

New stealth capability.

Inexpensive technology.

Can be made to operate on JP fuels.

Potential for high-energy missions.

Microturbine

Emerging.

Considered promising.

Not considered owing to lack of progress in producing workable systems.

Fuels.

Specific power.

System-specific energy.

Materials.

Cost.

Unknown