Solar Impulse is on standby for its first international flight this week. Brussels has been chosen as the destination for the first venture outside Swiss borders, which follows the solar powered aircraft's maiden flight and first overnight flight last year and will mark another important step towards the goal of flying around the world in 2012.

"Now, here we are in the definitive phase: it's no longer a question of tests, but the real thing," said Solar Impulse Chairman and round-the-world balloonist Bertrand Piccard. "And the next flights will not be made in the "familiar cocoon" of Payerne aerodrome, but in the whole of Europe…"

The Solar-Impulse prototype aircraft (designated HB-SIA) will be piloted from Payerne to Europe's 14th busiest airport in Brussels by CEO André Borschberg, who co-founded the project along with Piccard in order to show just how far renewable energies can take us.

"Flying an aircraft like Solar Impulse through European airspace to land at an international airport is an incredible challenge for all of us, and success depends on the support we receive from all the authorities concerned," said André Borschberg.

Developed by a team of 70 people and 80 partners over seven years, HB-SIA is a very impressive feat of engineering and, as you might expect from a plane that flies on the power of the sun, quite a lesson on just how much you can achieve with only a small amount of energy.

Keeping weight to a minimum is obviously critical and despite the aircraft's huge 63 meter (208 feet) wingspan, its carbon fiber frame and specially designed components weigh in at just 1600kg – which is a little like stretching your family car to be the width of an Airbus A340.

The wings carry almost all of the 11,628 solar cells on board, but even with more than 2000 square feet of photovoltaics, there's not a great deal of energy available to drive the four electric motors.

The Solar Impulse website breaks down the equation like this:

"At midday, each square metre of land surface, in the form of light energy, receives the equivalent of 1000 watts, or 1.3 horsepower of light power. Over 24 hours, this averages out at just 250W/m². With 200m² of photovoltaic cells and a 12 % total efficiency of the propulsion chain, the plane's motors achieve an average power of no more than 8 HP or 6kW – roughly the amount of power the Wright brothers had a available to them in 1903 when they made their first powered flight."

Eight horsepower. My lawnmower has more grunt, but then again it doesn't fly to heights of over 27,900 feet!

A second plane with better performance and a larger cockpit is under construction for the around the world trip.

After a stint in Brussels from 23 to 29 May, the aircraft will make its way to Paris for the 49th International Paris Air Show (20 to 26 June 2011) where it will be displayed both on the ground and in the air – flying demonstrations are planned each morning if the weather is favorable.

Solar Impulse at a glance:

  • Wingspan: 63,40 m (208 ft)
  • Length: 21,85 m (71.7 ft)
  • Height: 6,40 m (20.9 ft)
  • Weight: 1,600 Kg (3,527 lbs)
  • Motor power: 4 x 10 HP electric engines
  • Solar cells: 11,628 (10 748 on the wing, 880 on the horizontal stabilizer)
  • Average flying speed: 70 km/h (43.5 mph)
  • Take-off speed: 35 km/h (21.7 mph)
  • Maximum altitude: 8 500 m (27,900 ft)

The first international flight can be followed online at the Solar Impulse site.