That's pretty awesome, though I wonder how they achieved that efficiency from simple compressed air (surely a pack of Li-Ion batteries of the same volume would do better?).
Regardless, you can compress air yourself all day long using solar panels and/or wind turbines, and even if you use the grid, it'll still come out a lot cheaper...
The proposed benefits seem to mainly be in the ease of deploying the recharging infrastructure, not greater efficiency. Here's a paper that's skeptical of the overall efficiency: http://iopscience.iop.org/1748-9326/4/4/044011/fulltext/
Interesting paper, and it suggests some other possibilities, including a Pneumatic/Combustion hybrid (i.e. using a compressed air "flywheel") which seems to have greater benefits than an Electric/Combustion hybrid (a tank of compressed air is lighter than batteries).
Perhaps Tata is experimenting with an electric/pneumatic hybrid (so electric, but compresses air when braking, and consumes it when accelerating). This might work, but doesn't help with infrastructure rollout.
> a tank of compressed air is lighter than batteries
Joule for joule, it's not. The best compressed air tanks you'll find roughly reach lead/acid batteries in energy/weight (~100kJ/kg). Lithium-Ion batteries have 4 to 9 times the energy density.
Indeed. Also the mechanism to capture compressed air when braking would be in addition to the electric motor, which is needed in any event, and can charge batteries when braking. So yeah, upon reflection, just a Bad Idea.
Regardless, you can compress air yourself all day long using solar panels and/or wind turbines, and even if you use the grid, it'll still come out a lot cheaper...