Hi Scott

A few studies have shown a fuel-cell plane to be feasible-ish. And with a huge set of solar-wings a fuel-cell plane could have unlimited range via continual regeneration of its reactants. I think that's the rationale for the 'Eco-Flyer' which will be a round-the-world attempt in a couple of years. There are flexible solar-cells printed onto thin substrates which can now get 4,300 W/kg energy-density, so the weight penalty can be made low enough for flight.

Personally I'd like to see advanced solar-powered airships in the upper atmosphere - perfect for astronomy and wireless base-stations if they can be placed out of the stratospheric winds.

Adam

PS Are you a Ph.D? We could call you 'Dr. Evil' then.