Article originally published on Noria.com.
Energy efficiency must be measured in terms of the reduction of energy consumption. More specifically, it is related to how much energy the machine consumes in order to operate. This principle applies to machines that convert one type of energy like chemical or electric to a mechanical one, such as electric motors and combustion engines.
It is also applicable to machines that transmit mechanical energy, like gearboxes. In some cases, it may be evaluated in a powertrain such as a combination of a combustion engine and a transmission.