|In SI base units||kg·m−1s−3|
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.
Volume power density is sometimes an important consideration where space is constrained.
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.
|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|