There is a diagram in the article. The energy stored in the compressed gas is created and transferred with hydraulics. The compressed air is trapped in what is referred to as a hydraulic accumulator. Efficient enough.
Compressing air as a means of regenerative braking is fine, but it still isn’t efficient if they have to use the engine to compress air to run at low speeds.
Keeping smelly, visible pollution out of urban areas and dumping it out in the sticks makes libtards feel good.
“The compressed air is trapped in what is referred to as a hydraulic accumulator. Efficient enough.”
Now there is something I know a bit about. As a machinist and fabricator, I built and installed hydraulic accumulators into industrial machinery. They are a steel cylinder with a floating piston, with compressed air on one side, and hydraulic oil on the other. They don’t hold a great volume of compressed air and as I see it, would be useful mainly to give an underpowered car a quick boost in acceleration in heavy traffic. Such a device would not take you around the block!