You nailed it: there is a conflict between surface area (wanting more for solar charging) and efficiency (you want it to be aerodynamic and light, hence less area for solar charging).
I also think an extendable canopy (for a car, not a bike) should be a better approach. I wonder if anyone tried it.
I also think an extendable canopy (for a car, not a bike) should be a better approach. I wonder if anyone tried it.