Solar Impulse 1 – The Prototype That Flew Through the Night

Everyone remembers Solar Impulse 2 and its flight around the world. But the adventure started with a prototype: Solar Impulse 1, registration HB-SIA. Its job was to answer one question. Can a solar-powered plane fly through the night, keeping enough energy in its batteries to see the next sunrise?

HB-SIA has a wingspan of 63.4 m, about the same as an Airbus A340, yet it weighs only about 1,600 kg. The upper wing and the tailplane carry 11,628 solar cells rated at about 45 kW peak. Under the wing hang four nacelles, each with a lithium polymer battery, a 7.5 kW electric motor and a 3.5 m propeller. To save weight, the structure is a carbon-fibre honeycomb sandwich. The plane cruises at only about 70 km/h, slower than a car on the motorway.

After the first short hop in December 2009, the big moment came in July 2010: pilot André Borschberg stayed airborne for 26 hours, including about nine hours in darkness, powered only by the sun. In 2012 the plane made its first intercontinental flight, from Madrid to Rabat in Morocco. On the way from Switzerland to Madrid it set records for the longest solar flight between declared waypoints (1,099 km). In 2013 Bertrand Piccard and Borschberg crossed the United States in several stages, from California to New York.

Everything learned with HB-SIA went into the bigger HB-SIB, which circled the globe in 2015–2016. Today the prototype is on display at the Cité des sciences et de l’industrie in Paris. It sits in a line of solar aircraft that started with tiny pioneers like the Gossamer Penguin and the Solair I.

Technical data

Photos

• Top photo: David Lapetina / Wikimedia Commons, CC BY-SA 3.0
• HB-SIA during its US tour, after landing in Washington, D.C.… Photo: ENERGY.GOV / Wikimedia Commons, Public domain
• The very first "flea hop" in Dübendorf on 3 December 2009. Photo: Matth1 / Wikimedia Commons, CC BY-SA 3.0

Sources

• Wikipedia: Solar Impulse