Solar Impulse

Lore & Background

Bertrand Piccard initiated the Solar Impulse project in November 2003 after a feasibility study with the École Polytechnique Fédérale de Lausanne (EPFL). André Borschberg directed construction of each aircraft and oversaw flight mission preparation. By 2009, a multi-disciplinary team of 50 engineers and technical specialists from six countries had assembled, assisted by about 100 outside advisers and 80 technological partners. The project was financed by private companies and individuals, with around CHF 6 million from the Swiss government; backers included Omega SA, Solvay, Schindler, ABB, and Peter Diamandis.

Solar Impulse 1 (HB-SIA)

Technical expertise came from EPFL, the European Space Agency, and Dassault, while SunPower provided the photovoltaic cells. The first aircraft, Solar Impulse 1 (HB-SIA), was a single-seated monoplane with a non-pressurized cockpit and a wingspan similar to an Airbus A340. It carried 11,628 photovoltaic cells on the upper wing surface and horizontal stabilizer, powering four electric motors and charging lithium polymer batteries for night flight. The prototype was designed to remain airborne up to 36 hours.

Its first test flight occurred in December 2009. In July 2010, it flew an entire diurnal solar cycle in a 26-hour flight, including nearly nine hours of night flying. The aircraft completed flights from Switzerland to Spain and Morocco in 2012, and a multi-stage flight across the US in 2013. The second aircraft, Solar Impulse 2 (HB-SIB), completed in 2014, carried more solar cells and more powerful motors.

On 9 March 2015, Piccard and Borschberg began a circumnavigation from Abu Dhabi. By June 2015 the plane had traversed Asia; in July 2015 it completed the longest leg from Japan to Hawaii, during which the batteries sustained thermal damage and took months to replace. After a battery cooling system was installed, the circumnavigation resumed in April 2016, continuing across the US to New York City in June 2016, then crossing the Atlantic to Seville, Spain. It stopped in Egypt before returning to Abu Dhabi on 26 July 2016, 506 days after departure.

Reader's Guide

Solar Impulse demonstrated the feasibility of sustained solar-powered flight by a piloted fixed-wing aircraft, achieving the first circumnavigation of the Earth using only solar power. The project's significance lies in its technological achievements: the aircraft's photovoltaic cells and battery systems allowed it to fly through the night, and the second aircraft completed a 42,000 km journey over 17 stages in 16.5 months. The project also aimed to promote clean technologies, with Piccard stating the goal was to create a revolution in people's minds to promote solar energies. The aircraft's major design constraint was the capacity of its lithium polymer batteries; over an optimum 24-hour cycle, the motors could deliver a combined average of about 8 hp, roughly the power of the Wright brothers' Flyer.

In 2019, Solar Impulse 2 was sold to Skydweller Aero, a US-Spanish company developing autonomous unmanned aerial vehicles for perpetual flight. In May 2026, it crashed in the Gulf of Mexico and was destroyed. The project cost €150 million from its beginnings in 2003 until mid-2015, with an additional €20 million raised in late 2015 to continue the round-the-world flight.