As Bertrand begins his slow descent toward Washington D.C. one might wonder how it feels to be up there. Sure, he has some incredible views of the Appalachians and both he and André are always welcomed by blue skies and sunshine (I guess that’s the minimum for a solar airplane); but both pilots fly in physically challenging conditions. The cockpit is not pressurized, meaning that from 12’000 ft. they are required to wear an oxygen mask. Also given the high altitude, it can either get really hot at midday or really cold early morning or late evening. Their pilot suite is especially designed to balance their body temperature, but it’s not enough.

The cockpit of the solar airplane is insulated with a special high-performance polyurethane rigid foam. This is an innovative technology developed by Solar Impulse’s Official Partner, Bayer MaterialScience especially for the project’s extraordinary needs. Thirty Bayer MaterialScience researchers are engaged in the project, working in Germany to develop special materials for this unique airplane. The insulating foam has to withstand temperature fluctuations between – 58°F and +122°F (-50°C and +50°C).

Temperature fluctuations are not only a problem for the pilot but also for the batteries. There are four lithium-polymer batteries on the plane and each battery is made of seven cells. These cells are like human cells: they don’t like radical changes in temperature. Cold climates slow them down and hot ones can be dangerous. Bayer MaterialScience’s foam is used on each of the four motor gondolas both to guarantee battery efficiency and keep the plane safe.

Also, the pilots fly following visual flight rules (VFR), instead of instrument flight rules (IFR) which means that visibility from the cockpit is essential. The cabin window is made out of high-performance polycarbonate films that give high visibility and insulation properties thanks to the cushion of air between two polycarbonate films.

What is best about these technological developments is that they are slowly being adapted to real-world applications. For example, the polyurethane foam is particularly useful for energy efficiency purposes in new buildings, decreasing energy consumption by over 90%. It’s also ideal for refrigerator manufacturers thanks to the foam’s light weight and high insulation properties.  The polycarbonate film can be used in combination with solar cells or even in the transportation industry to reduce vehicle mass.

What we see above our heads is therefore not a simple solar airplane, but the result of in-depth scientific research, technological innovation and a strive for a cleaner future. As Bayer MaterialScience likes to say, “If a new material passes the “Solar Impulse test”, then it’s definitely transferable to other industries”.

It’s hard to visualize what a chemical company produces. For most of us, chemistry is just a synonym for one of those endless high school classes. You would sit through it with the prospect of doing crazy experiments while really all you ended up doing was memorize the periodic table.

But chemistry is a fascinating field and a key aspect of Solar Impulse’s capability to fly above our heads on its way to St. Louis. If André and Bertrand can fly the airplane Across America today, it’s thanks to the Solar Impulse engineers’ ability to find the perfect weight-efficiency ratio. Think about it, every 1 m² (11 ft²) of solar cells produces enough energy to carry 8 kg (17.6 lb.) – which is not a whole lot. It was therefore evident that the wingspan of the aircraft would have to be very large but that every single gram of additional material would have as light as possible.  

Solvay, a Solar Impulse Main Partner as well as the first company to have joined the project back in 2004, has provided Solar Impulse engineers with exactly those materials: lightweight, efficient and resistant. For example, the average screw is made out of steel - too heavy for our airplane. Solvay therefore developed specialized plastic screws and bolts and many other mechanical parts that are five times lighter than steel. But what is more incredible, is the specialized film Solvay produced to cover the solar panels.

We all know that a solar airplane is, by definition, powered by the sun. The process, you may or may not know, is similar to photosynthesis – plants’ chemical process of transforming sunlight into energy. But when we think of solar energy we often imagine those large, chunky panels that are multiplying on our cities’ roofs. Solar Impulse is powered by solar cells but very different ones.

Solar Impulse’s solar panels are an integrative part of the wing. They are the upper layer while also acting as the energy collector of the plane. The solar cells used for the panels are extremely thin, only 135 microns, but like all solar cells they are rigid, brittle and very sensitive. So how is it possible that they are bent into the shape of the wing? Thanks to Solvay’s film. The solar cells are strung together and made into panels, literally by hand, by our engineers. The process is very long and can take over 15 hours per panel, but Solvay’s film  that encapsulates the cells allows them to be bent without breaking while also protecting them from UV rays. For the second airplane currently under construction, this film will be both on top and underneath the solar cells, protecting them against moisture. See this blog if you want to know more about the panels.

To fly at night, Solar Impulse needs to store the energy captured during the day to power the motors at night. Lithium-polymer batteries are used for this and Solvay brought in its electrochemistry competences and solutions to improve battery efficiency by using electrodes and electrolytes.

A Solvay representative mentioned the company’s interest in further researching their film technology in its quest to find new lightweight solar energy production processes. If weight might not be an issue on your house’s roof, it certainly can be for many other tools and appliances that haven’t gone solar yet – contrary to our solar airplane. 

As André continues his descent toward Dallas Fort Worth International Airport, a flight that might set a new world distance record in the solar aviation category, innovation is definitely reaching new heights, but not only in America’s skies.

Schindler, a Solar Impulse Main Partner and world leading elevator and escalator manufacturer, is following Solar Impulse’s pioneering spirit, also vertically, but in a different way. Schindler heavily invested in a concept; a concept that became reality and is now being commercialized:  a solar-powered elevator.

A revolutionary achievement, Schindler’s solar elevator does not only reduce energy consumption, it can run entirely on sunlight. Furthermore, because of their capacity to run independently of the power grid, it allows them to function, undisturbed, in case of a power outage.

Prototype solar elevators were tested in Barcelona (Spain) and Switzerland in residential, low-rise buildings. The energy is collected by solar panels on the building’s rooftop while excess energy is stored in the Energy Storage Device (ESD) until needed. Backup power needs are provided by a one- phase grid connection, significantly simpler and more cost-efficient compared to standard three-phase connections.

The embedded Schindler engineers are the direct partnership link between Schindler and Solar Impulse, demonstrating the intense information and innovation exchange between the two companies. But Schindler’s contribution to the project goes beyond. Thanks to them and five other partners, Solvay, Bayer MaterialScience, Swiss Re Corporate Solutions, SunPower and the Swiss Confederation, this year’s Across America mission has come true.   

Today, in the quaint city of Bern, which also happens to be Switzerland’s capital, the Swiss Federal Council reinforced its support of the Solar Impulse project.  

Thanks to this, Solar Impulse will continue to benefit from the hangars in Dübendorf (where HB-SIB is being built) and Payerne (where HB-SIA is currently housed and where the test flights of HB-SIB will occur). In the meantime, Switzerland’s affiliation to the project provides the ideal platform to showcase the Helvetian innovative and entrepreneurial spirit.

It’s not by chance that Solar Impulse took flight in this miniscule country at the heart of the Alps. Switzerland has always heavily invested in education and research and is currently home to some of the best laboratories, Universities and technologically innovative SMEs in the world. In fact, the project started thanks to a feasibility study done by the Swiss Polytechnic University in Lausanne (EPFL) while the aircraft was built using a number of materials researched, tested and manufactured within the Confederation’s borders.

The celebrated little white cross superimposed on a red square will once again proudly fly, this time through American skies. Let’s hope we’ll be able to break out, at least once, from the usual clichés of chocolates, cheeses and banks to show another side of this dynamic landlocked country...