This fall, Swiss adventurer Bertrand Piccard and his team will begin test flights of a prototype of Solar Impulse, a sun-powered plane designed to circumnavigate the globe without burning a drop of oil. Piccard wants the project to demonstrate the potential of green technology, and he’s feeling the pressure. “We still have to prove that this plane will fly,” he says.

Led by CEO André Borschberg, the team has implemented major design revisions since announcing the project in 2003, such as bowing the wings to improve handling and substituting lightweight engines, but the basic idea is the same. Photovoltaic cells on the wings will gather solar energy, recharging the batteries that power its propellers.

Traveling at a leisurely, energy-efficient 45 mph, Solar Impulse will take three weeks to loop the world, landing every few days to change pilots and show off the technology to the public. Piccard hopes the sight of the plane in flight will prove that renewable energy can transform even the most energy-hungry human activities, sparking interest and investment in green tech across the globe.

Takeoff of the full-size plane is slated for 2011, but Piccard and Borschberg are currently focused on getting the prototype off the ground by September and working their way up to 36-hour overnight flights. “We have the plane,” Piccard says. “This is really the moment of truth.”