throughout the production of the plane
now have practical applications in everyday products, including electric cars,
high-performance yachts, portable electronics, refrigerators, fabrics, and even
nutrition, with input from Nestlé Health
Science to keep the pilots healthy during
long flights. “We didn’t have the feeling
that we were building a plane, it was working on a series of projects that needed
solutions,” adds Michel.
For every eight kilograms of structure on
the plane, an additional 30 watts of power
was required, as well as an additional one
square meter of photovoltaic cells.
These numbers are what made the
structure design the most difficult
challenge, as the plane needed to be
lightweight, but also hold a pilot, the
photovoltaic system, and batteries.
“How do you build a structure of this
dimension that is lightweight? We
had to be clever in design and material selection,” Michel explains.
The Solar Impulse is constructed
around a honeycomb structure,
allowing the wings to be comprised
of mostly air. Any parts that have traditionally been metal were replaced
with ultra-light polymer components.
Solvay’s polyphenylsulfone (Radel)
and polyamideimide (Torlon) are two
of these materials that lent themselves to the light design. Compared
to metal, with densities ranging from
2. 7 to 7. 9 kg/m3, the polymers from
Solvay have densities between 1.4
and 1.8 kg/m3.
On top of the wings are the plane’s
11,628 solar cells, each as thin as an average human hair. “Solar cells convert light
to energy, but they are delicate and need
to be protected from the environment they
operate in,” explains George Corbin, head of
research, development, and technology at
Solvay. To protect the cells, and to reduce the
impact of temperature variations and solar
radiation that occur while flying, Solvay’s
Polyvinylidene fluoride (Solef) and Ethylene
chlorotrifluoroethylene (Halar) polymers
were used to “encapsulate” the cells. This
resin is UV-resistant, waterproof, and is
extruded in a film that is 17 microns thin.
The other primary challenge was harness-
ing energy, transforming it to electricity,
and storing it in batteries. The bottleneck,
was the battery systems, not the solar cells,
as the team needed to improve the batter-
ies’ energy density, increase the speed of
charging, and extend the life cycle.
Over the period of a day, the sun
averages around 250 W/m² of energy.
When the sun is at its highest, each
square meter of land receives the
equivalent of 1.3 horsepower (hp)
of light, or 1,000 watts. The Solar
Impulse has 200 square meters of
photovoltaic cells, and with a 12%
efficiency of the propulsion chain,
the plane averages 8 HP or 6 k W of
power. “It is the most fabulous way
to fly, because the more you fly, the
more energy you have on board,”
says co-pilot Andre Borschberg.
This energy is then stored in
high-efficiency lithium batteries, which con-
tain PVDF (Solef) and Solvay’s electrolyte
component monofluoroethylene carbonate
(FIEC). These battery systems are what
allow the plane to continue flying at night.
“Human progress in flight has been amazing. Behind every milestone are pioneers,
inventors, visionaries, pilots, engineers,
designers, mechanics, and many other
professionals who make dreams become
reality,” says General John Dailey, director
of the Smithsonian’s National Air and Space
Museum. The next milestone for the Solar
Impulse is the flight around the world in 2015.
Moving forward, the project will encoun-
ter a new set of complexities and complica-
tions. “The flight across America was one
country and one language,” Gregory Blatt,
head of marketing and communications
explains. In 2015, the plane will be making
stops in countries across the world, and
communication may be a potential barrier.
Apart from communication barriers, there
are many other challenges the team must
overcome for the flight around the world,
like dealing with the effects of humidity on
a fully electric plane. Where the first plane
was not water-tight, a second plane is
being designed to meet the challenges of
flying longer distances, across the ocean,
and at higher altitudes.
As the new airplane reaches its final stages
of construction, the Solar Impulse consortium
continues to work together, bringing together
new ideas and innovations. The plane should
be fully assembled in early 2014 and will
begin flight testing in preparation for its journey around the world, to show once again,
just how far solar energy has come.
Dr. Moniz adds, “People are going to be
surprised at where solar is in ten years,
and not only in standard applications,
but in applications we don’t know yet.”
The technologies and innovations used
to power the Solar Impulse flight across
America and the future flight around the
world, all have practical applications.
“We look back ten years and think the
world looks really different today … but
when we look ten years ahead, we think
the world is going to look the same – it’s
not. These are technologies that will make
ten years from now look just as different as
it does when you look back ten years. We
will see the fruits of all these technologies
changing the world.”
Solar Impulse World Records:
• Absolute Height: 9,235 m ( 30,300 ft)
• Height Gain: 8,744 m ( 28,690 ft)
• Duration: 26 hours, 10 minutes, 19 seconds
• Free Distance: 1,116 km (693.5 miles)
• Straight Distance: 1,099.3 km (683 miles)