DUEBENDORF AIRFIELD (Switzerland) - IT HAS the wingspan of a Boeing 747 but weighs less than a small car. And it is powered entirely by the sun.

Adventurer Bertrand Piccard on Friday unveiled the Solar Impulse, which, with its sleek white wings and pink trimming, aims to make history as the prototype for a solar-powered flight around the world.

'Yesterday it was a dream, today it is an airplane, tomorrow it will be an ambassador of renewable energies,' said Mr Piccard, who in 1999 copiloted the first round-the-globe nonstop balloon flight. The plane will take part in a series of test flights over the next two years, and based on the results of those a new plane will be constructed for the big takeoff, in 2012.

In a swank ceremony at a military airfield near Zurich, Piccard and co-pilot Andre Borschberg hugged as the curtain was pulled across to give the public its first glimpse of the plane. Numerous dignitaries were in attendance, including Prince Albert of Monaco and major sponsors.

The budget for the project is 70 million euros (US$140 million), Mr Piccard said. He and Mr Borschberg said the plane will fly day and night using almost 12,000 solar cells, rechargeable lithium batteries and four electric motors. It will not use an ounce of fuel.

But the maiden flight around the planet will take time. With the engines providing only 40 horsepower, the plane will fly almost like a scooter in the sky. It will take off at the pedestrian pace of 35kmh, accelerating at altitude to an average flight speed of 70kmh.

Unlike the nonstop balloon trip, the solar flight will have to make stops to allow for pilots to switch over and stretch after long periods in the cramped cockpit.

'You can see it's really small,' Mr Borschberg said. 'Thirty-six hours is already a challenge. It tests your patience.' The plane's circumnavigation will be split up into five stages, with the stopovers also allowing the team to show off the plane. Mr Borschberg said the stages in the air will last up to five days.

A nonstop round-the-world flight will have to wait until batteries can be made lighter so more pilot comfort can be added to the plane. The first test flights will be later this year, with a complete night voyage planned for 2010.

In 1980, the fragile Gossamer Penguin ultra-lightweight experimental solar plane flew short demonstration flights with one pilot on board. A more robust project called the Solar Challenger flew one pilot from France to England in a five-hour-plus trip in 1981. -- AP