There are already planes that can fly (and do nothing else useful) on 300W/m^2 Solar panels already have sufficient mass power density. There's a pretty big ga

There are already planes that can fly (and do nothing else useful) on 300W/m^2 Solar panels already have sufficient mass power density. There's a pretty big gap between the 10s of MW a jumbo needs and the 700m^2 of area it has. If you were willing to trade some flight speed you could increase wing area 5x or so, and maybe make it work in the 2-4kW/m^2 range if all of the photons were at your bandgap.