In my opinion, there's not enough RC surface area for in flight solar power. Further, unless painted on, at 100+ MPH silicone cells may cause drag, peal off, or make unstable flight.
The full-scale F-15's I worked on used on-board generators. It appears on-board gen sets also exist for RC aircraft:
Some hobbyists are selling micro brushless gen sets up to 19000 RPM. If turbine shaft is accessible, it would probably need to be geared down before fitting the brush-less mirco gens.
No, not even close. It would take hours just to recharge batteries even if the entire plane was made of PV cells. Adding PV would reduce battery life due to the extra weight.