That said, even under the best circumstances, it takes a lot of time for the sun to recharge the batteries of a Sun Flyer. Bye Aerospace CEO George Bye tells Popular Science:

Solar panel efficiency of course varies with the time of day, the weather, the time of year, so there's several factors impacting how much the solar power contribution might be to the plane's batteries. If you're flying the airplane slowly, the amount of energy required to maintain flight, combined together with the best solar combination of clear, sunny skies and summertime, the solar energy contribution can be fairly significant, up to 20 percent of the energy required for flight, even a little bit more. If it's cloud and a winter time flight, the solar energy contribution diminishes.

In this sense, it's best to think of the Sun Flyer as an electric airplane, with the added bonus of solar power as one possible source of energy. In descent, the plane's propeller can also recharge the batteries somewhat, working like a windmill. Most of the time, the electric motor flies the plane running on power stored in batteries. For weekend flyers, especially those with the luxury of outside storage and sunny skies, the plane is closer to a purely solar powered vehicle than not.

Still, Bye is confident about what this means for the future. “We can fly and will be flying, not just trainers, but several kinds of general aviation aircraft in the coming five to ten years and beyond, and those technologies will certainly come to benefit larger aircraft as we progress,” Bye says, “As we progress, electric and hybrid aviation is very definitely in the future.”

For small aircraft, it's increasingly clear that solar power isn't just the future, it might even be the now.