Solar Impulse is a Swiss long-range experimental solar-powered aircraft project, and also the name of the project’s two operational aircraft. The privately financed project is led by Swiss engineer and businessman André Borschberg and Swiss psychiatrist and aeronaut Bertrand Piccard, who co-piloted Breitling Orbiter 3, the first balloon to circle the world non-stop. The Solar Impulse project’s goals were to make the first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power and to bring attention to clean technologies. Reflecting on these goals, Mike Scott wrote in Forbes magazine: “If we can fly around the world using only the power of the sun and the optimisation of energy efficiency technologies, the potential of clean technologies in other applications is immense.”
The aircraft are single-seat monoplanes powered by photovoltaic cells; they are capable of taking off under their own power. The prototype, often referred to as Solar Impulse 1, was designed to remain airborne up to 36 hours. It conducted its first test flight in December 2009. In July 2010, it flew an entire diurnal solar cycle, including nearly nine hours of night flying, in a 26-hour flight. Piccard and Borschberg completed successful solar-powered flights from Switzerland to Spain and then Morocco in 2012, and conducted a multi-stage flight across the US in 2013.
A second aircraft, completed in 2014 and named Solar Impulse 2, carries more solar cells and more powerful motors, among other improvements. On 9 March 2015, Piccard and Borschberg began to circumnavigate the globe with Solar Impulse 2, departing from Abu Dhabi in the United Arab Emirates. The aircraft was scheduled to return to Abu Dhabi in August 2015 after a multi-stage journey around the world. By June 2015, the plane had traversed Asia, and in July 2015, it completed the longest leg of its journey, from Japan to Hawaii. During that leg, the aircraft’s batteries sustained thermal damage that took months to repair. Solar Impulse 2 resumed the circumnavigation in April 2016, when it flew to California. It continued across the US until it reached New York City in June 2016. Later that month, the aircraft crossed the Atlantic Ocean to Spain. It stopped in Egypt before returning to Abu Dhabi on 26 July 2016, more than 16 months after it had left, completing the approximately 42,000 kilometre (26,000 mile) first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power.