Someday soon Bertrand Piccard is going to throw the switches on his Solar Impulse Foundation aircraft, tug back on the stick and pull it into the air. Then he’ll fly it right around the world. The impressive technology demonstrator’s just about to take its maiden flight. Let’s hope it’s not cloudy.

The Solar Impulse Foundation, cofounded by Piccard, has some loft goals about promoting research and innovative exploitations of renewable energy use in the aeronautics industry, getting the information and news about inventions out to the public, and promoting sustainable development. One route to doing this is to tackle the tricky challenge of flying around the world in a solar-powered aircraft, and that’s exactly what the SIF set out to do in 2003–with building starting in 2007.

Several weeks ago the impressive-looking vehicle, dotted with 12,000 individual photovoltaic solar cells underwent some initial engine power tests, and last week it rolled down the runway in Switzerland under its own power in some low- and high-speed taxi tests to test out controls, handling, and the delicate undercarriage. Under a test-pilots command, ground speed reached 10 miles an hour, and conditions were almost right for a first flight. Instead the team played it safe, and that flight should happen some time this week, if all goes well. Playing it safe sounds particularly sensible when you learn that the Solar Impulse is the size of an Airbus, but weighs about as much as a mid-sized car.

Of course solar-powered aircraft are nothing particularly new: NASA’s Pathfinder aircraft has been in the news for several years, and QinetiQ’s Zephyr aircraft broke some world records when it was demonstrated to the U.S. Air Force last year. But both of those aircraft are designed for specific tasks–mainly loitering around a specific location at very high altitude for defense or communications-node purposes–and they’re unmanned, which frees up their design to be very, very light.

Piccard’s vehicle is important because when it flies, it’ll be a very potent demonstration of how far solar-power technology has come: It’s efficient enough to fly a person into the air under power, and then fly that pilot around the world. Of course Piccard isn’t envisioning a future where we all hop into our solar sail-planes for the journey to work, pseudo-Jetsons-style. Instead it’s supposed to act as a symbol, “almost a provocation” as the Web site puts it, that solar technology could have a valuable role in aviation, an industry that many finger as being a serious eco-threat, with its almost exclusive reliance on fossil fuel. Fingers crossed then that the first flight–and more important the first landing–goes well this week, since Piccard’s six-year effort as resulted in just a single fragile airframe.