Solar cells on an A-380 -- or better a 787 -- could take some of the generator load off the engines and save fuel. At least if they weren't too heavy . . .
But except for maybe communications or surveillance platforms, solar aviation seems like something to think about after we've shut down all the fossil fueled power plants and are all driving electric cars. The Impulse is a great demonstration of solar in general, but I'm not convinced about solar aviation.