In energy transformers including batteries, fuel cells, motors, etc., and also power supply units or similar, power density refers to a volume. It is then also called volume power density, which is expressed as W/m3.
In reciprocating internal combustion engines, power density--power per swept volume or brake horsepower per cubic centimeter --is an important metric. This is based on the internal capacity of the engine, not its external size.
This section needs expansion. You can help by adding to it. (July 2015)
|Storage material||Energy type||Specific power (W/kg)||Power density (W/m3)|
|Hydrogen (in star)||Stellar fusion||0.00184||276.5|
|Supercapacitors||Capacitance||up to 15000||Variable|
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