Air Carrier Captain reports being dispatched on a ferry flight with one generator inoperative and the APU serving as the second generator. Once airborne the APU faults and will not restart. After consulting with Maintenance and Dispatch the decision is made to divert to an airport where repairs can be made.

Narrative

On taxi out for a ferry flight we had a right generator off light come on. We followed the checklist with no help as the light remained on. Got a 3 way phone patch with Dispatch and Maintenance to discuss the problem. It was agreed to defer the right generator and continue to destination. We received an updated Release and a new flight plan showing the deferral and fuel penalties. We accomplished the MEL deferral checklist (disconnecting the right IDG) with the APU running for the rest of the flight; and placed a def sticker next to the right generator control switch. After takeoff; into the flight no more than 5 mins; the APU shut down with the APU fault light on. We followed the checklist and were unable to restart the APU. Again; we got a 3 way phone patch with Maintenance and Dispatch. Another attempt to start the APU per Maintenance was tried but no help and still had the APU fault light on. It was agreed upon by Maintenance; Dispatch; and Captain to divert to ZZZ as that was the closest airport to fix the plane (as returning to the departure airport was not a feasible option as no maintenance was available). The rest of flight was uneventful.