Solar Aviation

The Solar Impulse is not the first solar airplane ever designed, but it is certainly the most ambitious. None of its predecessors has ever managed to fly right through the night with a pilot on board.

 

Solar aviation began with model aircrafts in the 1970s, when affordable solar cells appeared on the market. But it was not until 1980 that the first human flights were realized. 

Solar Aviation History

In the United States, Paul MacCready's team developed the Gossamer Penguin, which opened up the way for the Solar Challenger. This aircraft, with a maximum power of 2.5 kW, succeeded in crossing the Channel in 1981 and in quick succession covered distances of several hundred kilometers with an endurance of several hours. In Europe, during this time, Günter Rochelt was making his first flights with the Solair 1 fitted with 2500 photovoltaic cells, generating up to 2.2kW.

In 1990, American Eric Raymond crossed the United States with Sunseeker in 21 stages and 121 flying hours over a period of almost two months. The longest leg was 400 kilometers. The Sunseeker was a solar motorglider with a glide angle of 30 and an empty weight of 89 kg, and was equipped with amorphous silicon solar cells.

Icare 2

In the middle of the 1990s, several airplanes were built to participate in the ‘Berblinger’ competition. The aim was to be able to climb to an altitude of 450m with the aid of batteries and to maintain  horizontal flight with solar energy power of at least 500W/m2 , corresponding to about half of the power emitted by the sun at midday on the equator.

The prize was won in 1996 by Professeur Voit-Nitschmann’s team from Stuttgart University, with Icaré II (25 meters wingspan with 26 m² of solar cells.)

Helios

Even if it could not carry a pilot, one must not forget Helios, developed by the American company AeroVironment for NASA. This remote-controlled aircraft, with a wingspan of more than 70 meters, established a record altitude of nearly 30 000 meters in 2001. It was destroyed during flight two years later as a result of turbulence, and crashed into the Pacific Ocean.

In 2005, Alan Cocconi, founder of AC Propulsion, succeeded in flying an unmanned airplane (drone) with a 5-metre wingspan for 48 hours non-stop, propelled entirely by solar energy. This was the first time a device of this type was able to fly through a whole night, thanks to the energy collected by, and stored in, the solar batteries mounted on the plane.

Zephyr

From 9 to 23 July 2010, the Anglo-US company QuinetiQ made a non-stop flight of 336 hours, 22 minutes (14 days) with its drone Zephyr (27 kg, wingspan 12m), at an altitude of 21,562 m.

Solar Cells

I’ve already spoken about how HB-SIA collects and processes the energy from the sun and I’ve also linked it to the flight cycle, but I still haven't spoken about a much smaller but absolutely vital part for the functioning of the ...

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I’ve already spoken about how HB-SIA collects and processes the energy from the sun and I’ve also linked it to the flight cycle, but I still haven't spoken about a much smaller but absolutely vital part for the functioning of the aircraft: the solar cells.

There are currently 12’000 cells on HB-SIA’s wings and horizontal stabilizer. The next generation aircraft, HB-SIB, will have 15’000 of them. This might not sound so impressive until you know that the panel building process is all handmade. Yes, you got it; SunPower Corp. (NASDAQ: SPWR) provides the cells which are then put together, one by one, meticulously by our engineers, known as the Dübendorf boys.

I had the chance to see the unabridged process with my own eyes during one of my visits. I was in admiration of the engineer’s patience and constancy. For example, when a new batch of  solar cells arrive, each one of them needs to go through a final check before being tested, one by one, for their voltage three times. Can you imagine testing 15’000 solar cells thrice, that is, doing the same job 45’000 times!

If I am to run you quickly through the process, I can say that, after the healthy cells are promoted to the function “wing cell”, they will initially be stringed together into 300 cells, with a (+) and (-) pole on each end of the string (see solar energy article). This is followed by a layering process, placing a plastic resin under a glass foil, and so forth, eventually laminating the strings. The “sandwich” is then cooked at 95° for 7 hours before being placed on a mold that bends the cells into the desired shape, slightly rounded for the wings. What is most important during this long and tedious procedure is that nothing can fall on the panels before the curing process. Any microscopic piece of hair, dust or insect could potentially cause a short circuit, making the panel unusable and starting the process all over again with a new set of cells.  It takes 10-15 hours to make a panel and 48 of them are needed for HB-SIB alone; and that’s just the work involved in the solar panels…

To produce an aircraft that will take off and fly autonomously round the clock, propelled only by solar energy, is a tremendous challenge that requires the best and most reliable technology. SunPower’s Maxeon™ solar cell technology was selected because of its industry-leading efficiency and thickness of its solar cell. Each measures 135 microns, which is important for the power to weight ratio of the aircraft, and produces an efficiency of approximately 22.7%.

SunPower shares with Solar Impulse the values that have sustained SunPower since it was founded 27 years ago: a pioneering spirit, innovation, the human dimension, environmental awareness, in a world where solar energy can contribute to overcome the dependency on fossil energy and demonstrate that, by sharing the same vision, we can change the way the world is powered.

But let’s not get ahead of ourselves. What has been achieved is already an innovation in itself. 

Night-Flight Gains 3 World Records

The completion of what was ruled-out as impossible by many was not only a great achievement for the Solar Impulse founders and team of engineers, but it’s living proof for the project’s skeptics that the HB-SIA can indeed fly powered only by solar energy, and for 26-hours nonetheless!

Piloted by André, HB-SIA ...

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The completion of what was ruled-out as impossible by many was not only a great achievement for the Solar Impulse founders and team of engineers, but it’s living proof for the project’s skeptics that the HB-SIA can indeed fly powered only by solar energy, and for 26-hours nonetheless!

Piloted by André, HB-SIA whooshed through the skies. From afar it looked like a giant bird advancing with extreme nonchalance but the reality was very different. From inside the cockpit, André was well aware of the physical strain of staying awake 24 hours. In addition to the challenges of managing the ultra-light aircraft through gusts of alpine winds, André’s water source froze at high altitude. The team on the ground was tense as they feared the worst: not completing the world’s first solar night flight. But to their delight, André landed at the Payerne airfield 26 hours 10 minutes later looking as fresh as can be. Aside from the 5 o’clock shadow he was in better shape than the rest of the team!

This historic moment on 8 July 2010 resulted in, not one, not two, but three world records for HB-SIA and its pilot! The prototype aircraft was awarded records (in “Solar-Powered Aeroplane” category) for “Gain of Height” (8744m), “Duration” (26h 10min 19s) and “Absolute Altitude” (9235m).

Congratulations to HB-SIA, André Borschberg and the entire Solar Impulse team for the wonderful achievement!

Today the HB-SIA was sun-born

When I activated the solar cells of the HB-SIA during my second flight today, the aircraft not only started to produce electricity, ...

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When I activated the solar cells of the HB-SIA during my second flight today, the aircraft not only started to produce electricity, but it was also able to recharge its batteries. At this precise moment, when the Solar Impulse produced more energy than it was currently consuming, the fulfilment of a dream to fly solely on solar power, day and night came one step closer to reality.It was like a first encounter with the sun. After I had turned on the solar panel I could see the energy reserves increasing although the engines were continuously consuming power. Never before in my 40 years as a pilot have I experienced anything like this.I am exceptionally grateful for everybody who has supported us during the past seven years to put Bertrand's and my dream into action. Finally we can say we are flying a solar plane.

These thanks of course also go to our fans and followers, especially the proud "owners" of one of the 12000 solar cells who are part of our Supporters Program. You truly electrified me!


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