The future of compressors - Electric buses

It is a well known fact that the electric car revolution is underway. However the diffusion of electric buses will spread much faster than the one of electric cars. In 2040, 67% of buses on the road are expected to be electric. 

Unlike a passenger cars’ brake system, where they had to be changed into electrical controlled ones, in the case of trucks, the air brake system has been found to be the most stable and safe brake system.

But if there is no internal combustion engine to power the brake system then the compressor needs to be driven by a separate electric motor, as you can see on the following picture...