Compressed-air energy storage (CAES) is a way to store energy for later use using compressed air. At a utility scale, energy generated during periods of low demand can be released during peak load periods.
A pressurized air tank used to start a diesel generator set in Paris Metro
A compressed air locomotive by H. K. Porter, Inc., in use at the Homestake Mine between 1928 and 1961.
Schematic views of a nearly isothermal compressor and expander. Left view with the piston fully retracted, right view with the piston fully inserted.
Regenerative braking
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Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy or potential energy into a form that can be either used immediately or stored until needed.
The S7/8 Stock on the London Underground can return around 20% of its energy usage to the power supply.
A Tesla Model S P85+ using regenerative braking power in excess of 60 kW. During regenerative braking the power indicator is green.
The box extending sideways from the roof directly over the word "operation" allows air to freely flow through the resistors of the dynamic brakes on this diesel-electric locomotive.