The overall efficiency of a vehicle using
compressed air energy storage, using the above refueling figures, cannot exceed 14%, even with a 100% efficient engine—and practical engines are closer to 10-20%.
[6] For comparison,
well to wheel efficiency using a modern internal-combustion drivetrain is about 20%,
[7] Therefore, if powered air compressed using a compressor driven by an engine using fossil fuels technology, a compressed air car would have a larger carbon footprint than a car powered directly by an engine using fossil fuels technology.