We might imagine ceramic passivation coatings to protect surfaces of extra-low-orbiting birds. The ability to collect enough energy to drive thrust from large,

We might imagine ceramic passivation coatings to protect surfaces of extra-low-orbiting birds. The ability to collect enough energy to drive thrust from large, draggy solar panels seems like a limiting factor. Maybe they could double as wings? Keeping them oriented to minimize drag would interfere with their ability to collect energy. It might be the optimal geometry for such a bird would be a hollow cylinder with panels ranged all the way around the outer surface.