Zero fuel

Solar Impulse co-founders attempt the first round-the-world flight with alternative power

Lindsay James
18 November 2014

5 min read

The Solar Impulse team created the only airplane “able to fly day and night on solar power, without a drop of fuel.” Compass spoke to project co-founders and pilots Bertrand Piccard and André Borschberg about challenging the limits of sustainable transportation.

Swiss psychiatrist and aeronaut Bertrand Piccard has exploration in his blood. His grandfather, Auguste Piccard, was the first man to witness the curvature of the earth. His father, Jacques Piccard, traveled deeper into the earth than anyone else, diving to the bottom of the Marianas Trench – 10,916 meters (almost 7 miles) beneath the surface.

“Thanks to them, I met a lot of explorers and pioneers,” Piccard said. “I met Charles Lindbergh, Wernher von Braun, all of these inspirational people who made history. I wanted to have – like them – an interesting and useful life.”

Motivated by his early experiences, Piccard in 1999 achieved the first non-stop balloon flight around the world. “I started with 3.7 tons (3,700 kilos) of liquid propane and landed after 20 days and 45,000 kilometers with 40 kilos,” he said. “For the entire flight I was afraid that I wouldn’t have enough gas. I decided that the next time I flew around the world, I would do it without any fuel.” 


And so the idea for a solar-powered airplane was born. In the years that followed, Piccard spent countless hours working on his vision to circumnavigate the earth without fuel.

“In the 21st century, there’s a real need for new technologies to save energy,” Piccard said. “If you imagine a solar- powered airplane, which can fly day and night without any fuel at all, this is a demonstration that we can achieve the impossible with these new, clean technologies.”

In 2003, Piccard joined forces with Swiss entrepreneur and pilot André Borschberg, an engineer who graduated from the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts (USA) with a degree in management and science and has more than 20 years of flying experience in the Swiss Air Force. Together they founded Solar Impulse, a multi-disciplinary team of 50 specialists from six countries, assisted by about 100 advisors and 80 industrial partners, in a mission as challenging as it was visionary.

“To make an airplane fly day and night powered only by the sun, it needs to be extremely big in terms of wingspan,” Borschberg said. “Solar Impulse’s wingspan is 72 meters (236 feet), which is more than a Boeing 747. It also needs to be extremely light – 2,300 kilos (roughly 5,000 pounds), compared to approximately 333,000 kilos (734,000 pounds) for a 747.” 

“There was no benchmark,” Piccard added. “We had to develop, conceptualize and design a completely revolutionary prototype. Then construct it, operate it and fly it around the world. It is a really difficult project, but this is why we are so passionate about it.”

BERTRAND PICCARD (left), Initiator, Chairman and Pilot, and ANDRÉ BORSCHBERG (right), Co-founder, CEO and Pilot of Solar Impulse (Image © Solar Impulse | Ackermann |


Solar Impulse 1 was completed in 2010, built to demonstrate the concept’s feasibility. By making the first-ever 24-hour flight without fuel, the plane accomplished that task in July 2010. Solar Impulse 2, which will attempt to circle the world in 2015, needed to be more reliable, delivering greater performance with less energy. 

“Normally, if you build a new airplane you use existing engines; if you want to test new engines you use existing airplanes,” Borschberg said. “But here the propulsion is new. The type of energy is new. The structure is new. So, the level of complexity is incredibly high.”

3D technologies have been fundamental to the project’s realization. “When we were starting the design of the flight controls, we discussed it with an advisor who was very knowledgeable in designing aircraft,” Borschberg said. “We told him that we were only using 3D software to work out how to integrate the controls into the wings and the cockpit. He said: ‘You are totally crazy! Nobody has ever done that. You will have a lot of problems, build a mock-up first.’ We said that we didn’t have enough time and that we believed in what we were doing. So that’s what we did… and it was successful.” 

“Of course you might fail. So what? The worst is not to fail; the worst is not to try.”

Initiator, Chairman and Pilot, Solar Impulse

The team is now conducting final tests. “It flies very well, but the systems are very complex,” Piccard said. “We have the number of support systems we need to fly for five days and five nights. All of these have to work perfectly well. So we are continuing testing over the coming months.”

The around-the-world mission will take place over five months in 2015, from the beginning of March to the end of July. A host city is being identified in the Middle East, which will serve as the departure and arrival point.

The plane will circle the globe slightly north of the equator. To switch pilots, stopovers will be made in India, Myanmar, China, the USA and southern Europe or northern Africa. 

“We will wait for good weather patterns to cross the Pacific,” Piccard said. “That’s five days and five nights minimum. Crossing the Atlantic will take three to four days and nights without stops.”


The 35,000-kilometer (nearly 22,000-mile) flight requires rigorous training. Piccard and Borschberg will take turns piloting the aircraft, accumulating about 500 flight hours in the unpressurized 3.8 cubic meter (approximately 134 cubic feet) cockpit – equivalent to the cabin of a small car. 

“As we can only have one pilot on board at a time due to weight limitations, we need to make the pilot sustainable as well,” Borschberg said. “We need to meet the challenge of how to rest, how to feed ourselves, how to meet natural needs – all in the cockpit. We spend three days and three nights in the flight simulator under the same conditions as in the airplane, except for temperature and altitude variations. We can only rest for a very short period; up to 20 minutes, which are allowed thanks to the autopilot system. This helped us to understand how we behave, how we feel, when we get sleep deprivation.” 

The seat is designed to fulfill different purposes, such as a reclining berth and a toilet. Survival equipment is put into the seatback. “The cockpit is small, but big enough to do some exercises. I do yoga postures here in this volume,” Borschberg said. 

“Everything has been pushed to the limits.”

Co-founder, CEO and Pilot, Solar Impulse

Without air conditioning and heating, the pilots will face extreme temperatures: from 30°C to -20°C (86° to -4° Fahrenheit). Piccard and Borschberg will be protected by high-density thermal insulation foam built into the cockpit.

“We have two ways to get prepared,” Piccard said. “One is to test-fly the plane to be absolutely proficient. The other is all the simulations. Our mission team is running simulations on a regular basis with real weather patterns in order to have this plane in the best routes, best altitudes, best trajectories and best weather systems. We are now quite efficient in knowing how to do it, and we will implement all this knowledge for the real flight in 2015.” 

For both men, the project’s lure is to demonstrate how pioneering spirit, innovation and clean technologies can change the world. 

“If we can fly an airplane using the sun only as a source of energy, we can certainly use these technologies for energy savings on the ground as well,” Borschberg said. “(Developing) countries are facing huge challenges in terms of pollution, in terms of shortages, so it is one of the top questions that they have to solve.”

Piccard agrees. “The real impact I would like to see is that people will understand they can also reduce their energy consumption with cleaner technologies,” he said. “If you can produce energy from renewable sources without the use of fossil fuels, then you can completely change people’s lives.”

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