Solar Impulse: pushing technology to the limits

Engineers test the Si2 solar plane cockpit in the Ruag wind tunnel at the end of 2013 Fred Merz/Rezo/SolarImpulse/Polaris

Much more than a rich man’s toy, the Solar Impulse project is the driving force behind ground-breaking scientific innovations coming out of Switzerland’s most prestigious technological institution. 

Packed with cutting-edge technology, rather than becoming the plane of the future, the ambition of the Solar ImpulseExternal link project is to push the boundaries of science technology and reveal new possibilities of harnessing solar energy.

“The aim is to develop a strong symbol capable of attractively promoting pioneering spirit and innovation, of motivating people to challenge themselves to ambitious goals, in particular in the area of clean and renewable energy technologies,” said pilot and adventurer Bertrand Piccard when launching the project in 2003. 

Since its launch, the Solar Impulse project has been developed in collaboration with the Swiss Federal Institute of Technology Lausanne (EPFL)External link, where scientists and researchers from 20 different laboratories have been involved in the project. 

EPFL head of science for strategic partnerships Pascal Vuilliomenet says a project like Solar Impulse stimulates research by pushing scientists to their limits to create something that might otherwise not exist. 

“It also allows professors, assistants, and students from the different laboratories to work together and thus create links that might otherwise not be created,” he says. “It can also attract future potential students. For example, a high school student who doesn’t understand what a materials engineer can do, we can explain that to them with real examples.” 

Such examples can be found in the fact that the Solar Impulse needs to be both very light, and very solid to make its journey around the world using nothing but energy from the sun. Two separate laboratories at the EPFL have worked on optimising composite materials manufactured by Swiss companies North TPT, which produces base materials from a mix of carbon fibre and resin, and Decision SA, which builds structures with them.  

“It’s a bit like cooking: according to the piece you are trying to make, you need to cook it at certain temperature and pressure for a certain amount of time,” says Vuilliomenet. 

The result is that the structure of the Solar Impulse is lighter and more solid than what would otherwise be common. And the knowledge acquired during the research process can be commercialised by the two Swiss companies for use in other products such as ships or satellites. 

Maximum power

Making the plane as light as possible goes hand in hand with harnessing energy from the sun. While the 17,248 solar cells that cover the wings of the plane are not particularly revolutionary, they too have been stripped down to make them as light as possible. Unlike solar panels mounted on buildings, the panels on the plane cannot be encased in glass, so the EPFL has tested a new super light-weight, transparent and flexible plastic developed by Belgian chemicals giant Solvay. Again, the technological advances made in developing this material could have commercial applications in building construction. Solvay has also developed new components for batteries which increase their storage capacity by 10% while reducing their weight by 2%.  

Scientists at the EPFL have also applied themselves to the question of how the Solar Impulse can best use the small amount of power it does have. The results of their research into ways to optimise the flow of energy between the solar cells, batteries and motors were sent to Neuchâtel-based manufacturer Etel which was then able to develop motors with a yield of 96%. 

While it may only be a gain of a few points compared to current motors, it is still a record, says Vuilliomenet. 

“Without an exceptional project like Solar Impulse, we wouldn’t have invested the funds, the time or the energy necessary to achieve it, and then to extend it to the market as a whole,” he says. “And even if it is minimal, it is still interesting. It’s another brick of knowledge that will be available for use by others in other fields, perhaps outside of aviation, and so it could have a much more important impact.” 

Some impacts are less expected: Swiss manufacturer of elevators, escalators and moving walkways, Schindler, has just launched its first solar-powered elevator for which the energy management process was directly inspired by the company’s collaboration with Piccard and the EPFL. 

Wake up!

Yet another partner in the project, Swiss watchmaker OMEGA, has developed a converter to power the cockpit electronics – which function at a weaker voltage than the motors – that it says is “lighter, more compact and more efficient than other similar products available on the market”. 

Still in the cockpit, particular attention is paid to the body shape of the pilot, who must sometimes continuously stay at the controls for several days and nights without sleeping more than 20 minutes at a time. 

“They have sensors for monitoring breathing, heart rate, and brain activity, cameras which monitor the movements of the eyes and chin muscles,” explains Emmanuel Barraud, spokesperson for the EPFL. “What is new here, is that they have developed a micro-computer that is very light and very energy efficient that can calculate the data and tell with certainty whether the pilot is sleeping.” 

If the pilot blinks his eyes, it could simply be the effect of the sun or dehydration, but if at the same time the chin relaxes and the heart beat slows, he is sure to be sleeping, in which case the computer will activate an alarm. 

“This is technology that could be used in cars,” suggests Barraud. “Obviously we are not going to put on a helmet covered in electrodes every time we get behind the wheel, but even with just the eyes, we can capture some very interesting elements about the state of sleepiness in a driver.”

Translated from French by Sophie Douez