Solar aircraft can definitely be done (what with the existence proofs you provided) but they're not very practical. Power consumption is roughly proportional to the cube of speed, so to get the Solar Impulse 2's cruise speed up to, say, 150kts instead of the 49kts it actually does would require 27x more solar collection surface area. If you want to carry two people instead of one, it'll need to be about twice again as big. You'll hit annoying scaling laws since larger structures are proportionally weaker so it'll get even worse.