How efficient aMass Drivers?

Been working on the physics of mass drivers, with the limited
information I have. I've already calculated the amount of energy
required to launch a given payload into orbit given constraints of
acceleration and mass, but I'm assuming a 100% efficient system.

My questions:

Is there any data on how much overhead, above the kinetic energy
required for launch, is needed by the mass driver?

How much energy can be recovered by the deceleration phase?

This'll help me calculate how big a solar field is required.

Thanks