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Successful First Flight for Solar-Powered Electric Airplane

A rendering of the HB-SIA prototype above a commercial A340 to show comparison of wingspan and scale. Click to enlarge.

The Solar Impulse HB-SIA prototype electric aircraft made its first flight on 7 April. The goal of the Solar Impulse Project is to develop a solar airplane that can take off and fly, day and night, powered by solar energy alone around the world. In the flight, the Solar Impulse HB-SIA prototype climbed up to 1,200 meters, then flew for 87 minutes with test pilot Markus Scherdel at the controls.

A total of 11,628 monocrystalline silicon cells (10,748 on the upper wing surface, 880 on the horizontal stabilizer), each 150 microns thick, run four 7.5 kW (10 hp) electric motors and store the solar energy for the night in a 400 kg lithium-ion polymer battery system (25% of the weight of the plane). Each motor is mounted in a gondola beneath the wing which also contains a lithium polymer battery set and a management system controlling charge/discharge and temperature.

“This first flight was for me a very intense moment. The HB-SIA behaved just as the flight simulator told us. Despite its immense size and feather weight, the aircraft’s controllability matches our expectations.”
—Markus Scherdel

Thermal insulation conserves the heat radiated by the batteries and keeps them functioning despite the -40°C encountered at 8,500 meters. Each engine is fitted with a reducer that limits the rotation of each 3.5 meter diameter, twin-bladed propeller within the range of 200-4,000 rpm.

The prototype airplane has the wingspan of a large airliner (63.40 meters) and the weight of a midsize car (1,600 kilograms). With 200 m² of photovoltaic cells and 12% total efficiency of the propulsion chain, the aircraft’s motors achieve on average just 6 kW (8 hp)—roughly the amount of power the Wright brothers had available to them in 1903 when they made their first powered flight.

Solar Impulse is built round a carbon fibre-honeycomb composite using a sandwich structure. The upper wing surface is covered with a skin of encapsulated solar cells, and the undersides of the wings with a high resistance flexible film. 120 carbon fibre ribs placed at 50 cm intervals profile these two layers and give the body its aerodynamic shape.

Average flying speed is 70 km/h (38 mph); take-off speed is 35 km/h (19 mph).

Solar Impulse is supported by, among others, the Solvay group, Omega, and Deutsche Bank, who are its Main Partners. Bayer MaterialScience and Altran are the project’s Official Partners. The Ecole Polytechnique Fédérale de Lausanne (EPFL) is the Official Scientific Partner and Dassault-Aviation is the aircraft design and production Consultant.



Performances will be enhanced when solar cells get lighter but (2x) more efficient and batteries' weight is reduced 10 times or so.

An ultra light weight on-board fuel cell or high efficiency ultra light ICE genset could add range and procure low sunshine operation.

Very low noise Solar craft will soon be able to fly 24/7. Interesting for military and border surveillance purposes.


I'm sure the military is very interested in this. Drones that can surveil 24/7 would be important. Also for protecting the border.


It is very slow - it travels at 44mph which is too slow to hold a position against any serious wind.
I can see batteries getting better as the whole of the EV world is trying to make them lighter and higher capacity.

I do not see the solar cells getting better as no-one else really wants / needs very light solar cells.

It is also, presumably very, fragile and hard to fly (especially to land).

It is an interesting project, but I do not see solar powered aircraft being very important any time soon - there just isn't the energy density in sunlight.

A solar powered aircraft could have almost infinite endurance, but could get blown off position: but a solar assisted aircraft (with a sizable amount of chemical fuel for maneuvering) could be workable with (say) a 7 day endurance.


Useful for some military applications perhaps; but, it will be a long time before this technology will be commercially viable to move freight or people. Here again, just like BEVs, this application will depend greatly on the advance of battery technology and how soon the newer batteries can be mass produced.

In my opinion, we should move huge funds immediately to American battery development and production companies because batteries is the key element to the U.S. maintaining its society in the future.


Good points Lad. USA must get involved in continuous battery development and early mass production because importing batteries instead of oil would be nothing more than a change of external suppliers. However, it is doubtful if USA can compete if too many UAW highly paid members are involved. Very high level of factory automation may be required.

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The fact that this plain could fly for 87 minutes carrying a human pilot (not an UAV) and to a height of 1200 meters is a huge achievement. It may even be a world record for an electrically propelled aircraft with a pilot. Their website say they aim to do a 36 hours flight with this airplane sometime in 2010. They will build another airplane to be ready by 2012 that hopefully will be able to achieve their end goal of flying around the world near equator. They should specify explicitly whether that goal is with a human piloted aircraft or just with an UAV version of the aircraft. I believe it is with a human because their current plane has a cockpit and they plan to land the 2012 plane 5 times during the around the world flight and that would only make sense in order to change pilots.

I speculate that the 2012 plane will not use its current solar cells but will use a new type of thin-film, non-silicon based multi-junction cell that Sharp has developed and that will go into mass production in 2011 at a new Italian factory. These cells from Sharp are lightweight and have 35.8% conversion efficiency. That would enable a smaller, faster and less fragile 2012 plane which is probable necessary for an around the world flight. The 2012 plane should to be able to handle less than perfect weather as it does not appear that the current one can handle just a little bit of bad weather.

Sharp originally developed their triple-junction cells for earth-orbiting-satellites but are aiming to bring them to use at more “down to earth products”. The following quote from Sharp is telling “Sharp’s achievement of 35.8 percent efficiency on a “triple-junction compound solar cell” paves the way for this solar technology to find additional uses here on Earth. Engineers foresee installing them on airplanes and ships, for starters, and Sharp compound cells recently powered a car to victory in the world solar car race, with a top speed of 123km/h. Looking ahead, compound solar cells will be a key to ramping up utility-scale “concentrated solar” electricity production, in addition to expanding orbiting applications. “We’re moving from space to the ground,” says Tatsuya Takamoto, a senior Sharp engineer who led the compound solar cell development.”

As I see it solar cells has a great future for transportation of all sorts (airplanes, ships, cars and trucks) as they are the only mechanism known that can add substantial energy to a moving object without using fuel. For example, imagine you could wrap the entire body of Nissan’s Leaf with Sharp’s 35.8% solar cells. In sunny weather that could add 1790 Watts (= 1000W*0.358*5sqm) to supplement the battery or comparable to extending the range of the Leaf with 10-15%!

More info


Eventually (2030++?) , higher efficiency (over 50%?), much lower cost (well under $1/Wh) solar power energy converters will be mass produced. Those converters will also be very thin, flexible and very light weight. When integrated into cars, buses, trailers, e-trains, aircraft, boats, ships and other machines outer bodies and/or garage roof, solar power could supply an interesting percentage of the power used and/or keep the batteries charged.

When total car weight have been reduced by 50% and more and batteries by 80% and more, Plug-in solar e-cars may become a reality, specially in very sunny areas. Future e-cars will look very different than current ICE monsters.


I like PV as a range extender for vehicles, but realistically, given the solar-powered-vehicle races across Australia, these will still primarily be plug-in BEV, or PHEV.

The optimized solar racers have very low mass, Cd and frontal cross sections, and with similarly expensive triple-junction PV cells end up costing a million dollars or so.

Using very, very rough numbers...

If you put cheaper triple junction thin-film cells all over a Prius or Tesla or Volt or somesuch, you add at least $20K to the price, but the reward is maybe 1-2 Kilowatt-hours per day...maybe 4-8 miles per day, or 1,200-3,000 miles per year (lattitude and cloud cover depending). I'm guessing over 10 years, those cells return a cost of 67 cents per mile in a sunny climate. Does that seem realistic?

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In most places in the USA the sun delivers about 1000 Watts per square meter. If the Leaf got 5 sqm of Sharp’s 35.8% efficient solar cells it could produce 1790 Watts (= 1000W*0.358*5sqm) in sunny weather. Assuming 5 hours of sunlight on average each day and the Leaf could produce 5*1790 = 9 kWh of energy per day or enough to drive 9/0.24 = 37.5 miles per day. It is not economical. It will cost at least 10,000 USD for this extra EV feature but it is so cool that many people will buy it anyway. In countries near equator where the gasoline fueling infrastructure is limited and the sun shines a lot all year round such solar powered vehicles may in fact be the least costly way to get around in comfort.

Sharp’s Italian triple-junction solar cell factory will do 160MW in 2011 and 500MW per year in 2016. 500MW will be enough for 280,000 (=500M/1790) self-powered Leafs per year.


Solar e-cars would need maximized exposed areas. About 8 sq. m with larger roofs, hoods, trunk lids, front and rear windows should be possible. Roll out solar panels could increase exposed areas from 8 sq. m to 16 sq. m when parked. Solar cars equipped with larger 50% panels could collect about 3 to 4 Kwh/h while driving and up to 8 Kwh/h when parked in bright sunshine. This type of BEV would not have to be plugged in very often unless you do a lot of night driving. Ideally, a solar e-vehicle should be able to be driven with solar energy 5 to 6 hours every sunny day by 2030.




Your 1000W*0.358*5sqm isn't quite right. You forgot to multiply by the sinus of the angle the sunrays have with the panels. Plus, if you have sun on the right side of the car, the panels on the left side produce next to nothing.
So it's even less economical than you said.
That said, I do agree that people could buy it just because it's cool ant not because it's dollar-efficient.

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Simodul you are right. I might have been a bit too optimistic about getting 5 square meters of effective solar space on the car. I imagine it will be practical to put solar panels on the car’s roof, its doors and its front and back hood (if any). Inside the car you could get extra panels by putting them on the sun visors at the front and such visors could also be installed at other windows in the car. It is probably more realistic to say that 4 square meters of effective panels is possible on a normal sized car and you will probably need to fit up to 7 square meters of solar panels on the car to get that.

One drawback of such a car is that it will only come in one color which is solar cell black. Also it will be really expensive but really cool too to drive a car that produces its own fuel at least at summertime and near equator possibly all year round.


One drawback of such a car is that it will only come in one color which is solar cell black.

Actually the reflected color of solar cells is blue since they tend to absorb as much green light as possible which is the strongest part of the solar spectrum.

Technology has now enabled us to choose our solar cells thanks to the development of Dye Sensitized Solar Cells (DSSC). Instead of relying on just metal oxides inside the DSSC, different dyes and sensitizers have been included for reduced cost and added color.

How would you like your car to be glitter red? This cell is still 14.5% efficient.


@ Ai Vin,
Dye Sensitized cells are very low efficiency for the near-medium term.


Yes they are: But they are not the only way to get colored solar cells. The "glitter red" cell I linked to is 14.5% efficient and 'Bluesky Open Paradise Co.' is only one company. 'Lof Solar makes' cells that are more than 15% efficient and they come in many different colors;

The secret is that a "color" can be defined by a VERY narrow band of wavelength, so narrow that reflecting it to get the color you want to see isn't going to reduce the energy the cell takes in by much at all. In fact the cell can use all the wavelengths of light it does take in anyways and converts the extra energy into heat. It would be better for the cell if you could filter out(or reflect) the unused wavelengths before they became heat.


Correction: "In fact a solar cell CAN'T use all the wavelengths of light it does take in anyways and converts the extra energy into heat. It would be better for the cell if you could filter out(or reflect) the unused wavelengths before they became heat."

Will S

Some amount is reflected based on the reflectivity of the surface.

Peter Olorenshaw

This is just silly - why don't they use a lighter than air aircraft - ie an airship - lots of room for light but low efficiency solar cells, no issues with what to do do at night, or if you run out power...And you should be able to fly at 150kph.

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