The Solar Impulse 2 could fly around the world without a drop of fuel

The first time we flew around the world, it was 1924 and it took four pilots 175 days to do it. Flash forward some 90 years, and an ambitious crew in Switzerland is planning to take a stab at it themselves next year. The difference? They're aiming to do it in a plane that's powered solely by the sun.

That gangly, skeletal plane up there is the Solar Impulse 2. Its wings stretch nearly 240 feet tip-to-tip, and the whole (incredibly light) thing is festooned with over 17,000 solar panels. As it turns out, you can't actually wring that much horsepower out of all those solar cells -- the plane's top speed while at its maximum cruising altitude is a relatively pokey 88 miles per hour. That's like circumnavigating the globe in a Mazda. Of course, this machine wasn't built to break speed records -- it's all about the efficiency needed to keep the Impulse 2 in the air for up to a week at a time. All that means pilots Bertrand Piccard and André Borschberg are in for an arduous ride, even considering the plane has to touch down occasionally so one man can replace the other in the pilot's seat (which naturally doubles as the toilet). All told, their sojourn will last something like 20 full days of flying spread out over the course of a few months. Thankfully, the pair already has transcontinental test flights across Europe and the United States under their belts.

Would a successful trip pave the way for a new age of solar-powered sky cruising? That seems a little unlikely, but it would ensure a spot for Piccard and Borschberg in the annals of aviation history... and it just may get some more people excited about renewable energy.