The solar plane has the wingspan of a Boeing 747

It has the wingspan of a Boeing 747 but weighs less than a small car – and could be the first plane to fly around the world powered entirely by the sun.

This is the Solar Impulse, unveiled in Switzerland, which its inventor hopes will revolutionise air travel and reduce its impact on the environment.

Prospective passengers might need some convincing, however, that it is capable of staying up in areas where the sun picks and chooses its moments, ie, Britain.

Not adventurer Bertrand Piccard and Andre Borschberg, though, they are the pilots of this ground-breaking craft, making them possibly the bravest in the world.

Bertrand Piccard and co-pilot Andre Borschberg are set to begin tests

They are planning to prove the airplane’s viability with a round-the-world trip, although the scheduled take-off date, 2012, suggests they are in for a few more turbulent test flights.

He said: ‘Yesterday it was a dream, today it is an airplane, tomorrow it will be an ambassador of renewable energies.’

The plane, part of a £70million project, will fly day and night using almost 12,000 solar cells, rechargeable lithium batteries and four electric motors.

The engines provide just 40 horsepower so the plane will take off at 22 mph, accelerating at altitude to an average flight speed of 44 mph.

The Solar Pulse was unveiled in Switzerland

Unlike the first nonstop round-the-globe balloon trip which Mr Piccard co-piloted in 1999, the solar flight will have to make stops to allow for pilots to switch over and stretch after long periods in the cramped cockpit.

The first test flights will be later this year, with a complete night voyage planned for 2010.

Mr Piccard, 51, who comes from a family of adventurers, said: ‘It will be like the Wright brothers.

‘We will start one metre above the ground, then three metres, then five metres. When that works, we’ll be able to take it to altitude.’

But the solar plane cannot fly in bad weather because the solar panels are needed for day flying and for charging the 400-kilogram lithium batteries that power the plane by night.

Mr Borschberg said: ‘We’ll certainly avoid stormy situations. We’ll avoid rain as well, because you cannot collect energy in this weather. So the challenge for the team will be to find a path that is favorable.’

Mr Piccard says the plane should also serve as an inspiration for inventors and manufacturers of everyday machines and appliances.

‘If an aircraft is able to fly day and night without fuel, propelled solely by solar energy let no one come and claim that it is impossible to do the same thing for motor vehicles, heating and air conditioning systems and computers.’

Via Daily Mail