Contour modulation is a technique in which a phase-modulated signal waveform and amplifier output impedance work together to maintain higher efficiency over a sizable output power back-off.

To pump energy back into the grid, some of the rotational energy is bled off to power a generator on the main shaft.

Even when the car is off and locked, these fans whir around, so when you step back into it you don't need to crank up the power-hungry air conditioning.