Interesting hybrid engine which stores potential energy in compressed air instead of batteries like the Prius. There have been a bunch of alternative energy system that promised compressed air drive. This one seems more realistic although in the test-bed phase only.

The concept is simpler than that of an electric hybrid: the new hybrid engine has a compressed air tank connected to the engine instead of a battery unit. When required, e.g. when starting from rest or after changing gear, compressed air flows into the engine through an electronically controlled valve. If fuel is also injected, the engine responds quickly. Although the system used to control the valve is also technologically complex, this challenge can be mastered nowadays thanks to powerful algorithms and computer systems.