Swiss adventurer Bertrand Piccard unveiled Friday the prototype of a solar powered plane he plans to fly around the world to highlight the potential of alternative energy sources.

The prototype, HB-SIA, has the wingspan of a jumbo jet but weighs only as much as an average family car.

The propeller plane is powered by four electric motors and designed to fly day and night by saving surplus energy from its 24,000 solar cells in high-performance batteries.

Yesterday it was a dream. Today it is a plane. Tomorrow it will be an ambassador of renewable energy, Piccard told a news conference at Duebendorf airfield near Zurich.

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

Piccard, who made history in 1999 by flying round the world non-stop in a hot-air balloon, hopes the prototype will make its first test flights later this year before a first complete night flight in 2010 over Switzerland.

Friday's launch came after six years' work by 50 engineers and technicians on the so-called Solar Impulse, which has a number of high profile backers including Deutsche Bank, watchmaker Omega and Swiss chemicals maker Solvay and a budget of 70 million euros ($97.53 million).

The plane combines innovative aerodynamic features, novel light-weight materials strong enough to resist pressures at high altitude and solar technology.

A planned successor, HB-SIB, will likely be even bigger, enabling Piccard and fellow pilot Andre Borschberg to fly around the world along a path similar to the one he took in his Orbiter 3 balloon a decade ago.

HB-SIB will first fly across the Atlantic and the United States and is projected to start in 2012.

The pilots will spend 36-hours in the plane's tiny one-man cockpit and fuselage in initial flights to test its ability to fly overnight.

The round-the-world attempt will be made in five stages, each lasting several days, with Piccard and Borschberg sleeping for 15 minutes every two to four hours and using resting techniques such as auto-hypnosis and meditation to stave off fatigue.

Through this project we are proclaiming our conviction that a pioneering spirit and political vision can together change society and put an end to fossil fuel dependency, Piccard said.

The adventurer said it was important to find ways for business to make profit from sustainability to encourage investment and the development of alternative energies.

Josef Ackermann, chairman of Deutsche Bank, which manages 3 billion euros in sustainability-related investment products, told Reuters he saw big growth opportunities in renewable energy and ecologically friendly projects.

To have branding in these projects and be a leading force is very important for us. We see tremendous business potential going forward, Ackermann told Reuters.

(Editing by Louise Ireland)