Re: @James 51
"Even if we don't jump straight to all solar planes, they might inform the design of the next generation of planes."
This is the best point about all of this. Large, fully solar-powered planes are way, way off, maybe even an impossibility. But hybrid planes are a more realistic concept. Current planes spend much of their time above the cloud layer and have a large amount of real estate available on which to place solar panels. I can certainly see a future where jet-powered planes take off and reach cruising altitude, where they begin to harvest solar energy. They could then use it to boost engine performance and power the in-flight entertainment systems etc.