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Solar-powered plane ready for first international flight


May 2, 2011

HBSIA during flight testing in Switzerland (Photo: Solar Impulse)

HBSIA during flight testing in Switzerland (Photo: Solar Impulse)

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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.

About the Author
Noel McKeegan After a misspent youth at law school, Noel began to dabble in tech research, writing and things with wheels that go fast. This bus dropped him at the door of a freshly sprouted Gizmag.com in 2002. He has been Gizmag's Editor-in-Chief since 2007. All articles by Noel McKeegan

This is really interesting. Hope some day planes worldwide would be able to use this renewable energy source to fire their planes.

Ile Algernon

Great achievment and the around the world flight is a real challange. Maybe it would help to follow the sun during the day and then turn to east at sunset to make the night shorter? It would mean a longer flight time but more of the time with sunshine. But probably using the jetstreams are more important.

Kenneth Palmestål

Photovoltaic cells 12% efficient? I read 7 years ago they had reached 42%. I guess you can\'t trust claims until they are made commercially available. Even so, latest ads for off the shelf is 17%. I can\'t trust ads either.


The cells on the plane are made to be light and flexable that cuts into efficentcy. 42% has been achived but thats a prototype Rollsroce of a solar cell that would be to heavy and fractous for flight.

Joseph Mertens

A journey of 10,000km starts with a single step. If the developmental path of these planes follow that of regular flight, then we could have the first entirely solar powered commercial airplanes before the middle of this century. Of course, that\'s assuming no major developments in light-weight, high-efficiency solar panels & storage technologies. Personally, I wouldn\'t be surprised if-in the future-the solar cells will be used to convert water to hydrogen & oxygen, then use the hydrogen in fuel cells to create the motive power for the aircraft.


4 x 10 HP electric engines seems to be great for now .. hoping for better to come with the larger version of it

Chirag D Soni


The article refers to \'12 % total efficiency of the propulsion chain\' which would, I believe, not exclude higher PV efficiency, even say 20%. Before the electrical energy gets to the propellors there are other efficiency losses that would occur.

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