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 balloonist 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.Div, Stav. "Solar Impulse 2: The groundbreaking aircraft demonstrating the possibilities of clean energy", The Independent, 2 June 2016
The aircraft is a single-seated monoplane powered by photovoltaic cells; it is capable of taking off under its own power. The prototype, often referred to as Solar Impulse 1 (registration HB-SIA), 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."Swiss solar plane makes history with night flight". Swisster.ch. 8 July 2010. Retrieved 13 July 2010. 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 (registration HB-SIB), 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 and took months to replace.
A battery cooling system was installed and Solar Impulse 2 resumed the circumnavigation in April 2016, when it flew on to California.Berger, Noah. "Solar-powered plane completes journey across Pacific Ocean" , The Charlotte Observer, 24 April 2016 It continued across the US until it reached New York City in June 2016. Later that month, the aircraft crossed the Atlantic Ocean to Seville, Spain.Amos, Jonathan. "Solar Impulse completes Atlantic crossing with landing in Seville", BBC, 23 June 2016 It stopped in Egypt before returning to Abu Dhabi on 26 July 2016, more than 16 months after it had left (506 days), completing the approximately first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power.Amos, Jonathan. "Solar Impulse: Zero-fuel plane lands in Cairo", BBC, 13 July 2016"Solar Impulse completes historic round-the-world trip", BBC, 26 July 2016
In 2019, Solar Impulse 2 was sold to Skydweller Aero, a US-Spanish company using the airframe to develop autonomous unmanned aerial vehicles capable of perpetual flight. In May 2026, it crashed in the Gulf of Mexico and was destroyed.
Project development and funding Bertrand Piccard initiated the Solar Impulse project in November 2003 after undertaking a feasibility study in partnership with the École Polytechnique Fédérale de Lausanne (EPFL). As a mechanical engineer, co-founder André Borschberg directed the construction of each aircraft and oversees the preparation of the flight missions. By 2009, they had assembled a multi-disciplinary team of 50 engineers and technical specialists from six countries, assisted by about 100 outside advisers and 80 technological partners.
The project is financed by a number of private companies and individuals, as well as receiving around CHF 6 million (US$6.4 million) in funding from the Swiss government. The project's private financial backers include Omega SA, Solvay, Schindler, ABB and Peter Diamandis. The EPFL, the European Space Agency and Dassault have provided technical expertise, while SunPower provided the aircraft's photovoltaic cells.; and
Piccard stated that the entire project from its beginnings in 2003 until mid-2015 had cost €150 million. It raised another €20 million in late 2015 to continue the round-the-world flight.Al Wasmi, Naser. "Exclusive: Solar Impulse headed back to Abu Dhabi the long way round", The National, 8 January 2016
Timeline 2002:Solar Impulse. 2020. Solar Impulse - Around The World To Promote Clean Technologies. [online] Available at: <https://aroundtheworld.solarimpulse.com/our-story/milestone-feasibility-study> [Accessed 10 March 2020]. Feasibility study at the École Polytechnique Fédérale de Lausanne 2004–2005: Development of the concept 2006: Simulation of long-haul flights 2006–09: Construction of first prototype (HB-SIA; Solar Impulse 1) 2009: First flight of Solar Impulse 1 2009–11: Manned test flights 2011–12: Further test flights through Europe and North Africa 2011–13: Construction of second prototype (HB-SIB; Solar Impulse 2) 2013: Continental flight across the US by Solar Impulse 1 2014: First flight of Solar Impulse 2 2015–2016: Circumnavigation of the Earth by Solar Impulse 2, conducted in seventeen stages over 16-1/2 months
Solar Impulse 1 (HB-SIA)
The first Solar Impulse aircraft, registered as HB-SIA, was primarily designed as a demonstration aircraft. It has a non-pressurized cockpit and a single wing with a wingspan similar to that of the Airbus A340 airliner. Under the wing are four nacelles, each with a set of lithium polymer batteries, a electric motor and one twin-bladed propeller. To keep the wing as light as possible, a customised carbon fibre honeycomb sandwich structure was used. 11,628 photovoltaic cells on the upper wing surface and the horizontal stabilizer generate electricity during the day to power the electric motors and to charge the batteries allowing flight at night, theoretically enabling the single-seat plane to stay in the air indefinitely.
The aircraft's major design constraint is the capacity of the lithium polymer batteries. Over an optimum 24-hour cycle, the motors can deliver a combined average of about , roughly the power used by the Wright brothers' Flyer, the first successful powered aircraft, in 1903. In addition to the charge stored in its batteries, the aircraft uses the potential energy of height gained during the day to power its night flights.
Specifications
Operational history
Maiden flight and other early flights
On 26 June 2009, Solar Impulse 1 was first presented to the public at the Dübendorf Air Base, Switzerland. Following taxi testing, a short-hop test flight was made on 3 December 2009, piloted by Markus Scherdel. Borschberg, co-leader of the project team, said of the flight:
On 7 April 2010, the plane conducted an 87-minute test flight, piloted by Markus Scherdel. This flight reached an altitude of . On 28 May 2010, the aircraft made its first flight powered entirely by solar energy, charging its batteries in flight.
First overnight flight On 8 July 2010, Solar Impulse 1 achieved the world's first manned 26-hour solar-powered flight. The airplane was flown by Borschberg, and took off at 06:51 Central European Summer Time (UTC+2) on 7 July from Payerne Air Base, Switzerland. It returned for a landing the following morning at 09:00 local time. During the flight, the plane reached a maximum altitude of . At the time, the flight was the longest and highest ever flown by a manned solar-powered aircraft; these records were officially recognized by the Fédération Aéronautique Internationale (FAI) in October 2010.
International and intranational flights
Belgium and France (2011)
On 13 May 2011 at 21:30 local time, the plane landed at Brussels Airport, after completing a 13-hour flight from its home base in Switzerland. It was the first international flight by the Solar Impulse, which flew at an average altitude of for a distance of , with an average speed of . The aircraft's slow cruising speed required operating at a mid-altitude, allowing much faster air traffic to be routed around it. The aircraft was piloted by Borschberg. The project's other co-founder, Piccard, said in an interview after the landing: "Our goal is to create a revolution in the minds of people...to promote solar energies – not necessarily a revolution in aviation."
A second international flight to the Paris Air Show was attempted on 12 June 2011, but the plane turned back and returned to Brussels because of adverse weather conditions. In a second attempt on 14 June, Borschberg successfully landed the aircraft at Paris' Le Bourget Airport after a 16-hour flight.
First intercontinental flight (2012) On 5 June 2012, the Solar Impulse successfully completed its first intercontinental flight, a 19-hour trip from Madrid, Spain, to Rabat, Morocco. During the first leg of the flight from Payerne Air Base to Madrid, the aircraft broke several further records for solar flight, including the longest solar-powered flight between pre-declared waypoints () and along a course ().Solar Impulse’s HB-SIA obtains two new world records . SolarImpulse.com. 26 September 2012. See also: FAI Record ID #16558 and FAI Record ID #16560 .
United States (2013)
On 3 May 2013, the plane began its cross-US flight with a journey from Moffett Field in Mountain View, California, to Phoenix Goodyear Airport in Arizona. Successive legs of the flight ended at Dallas-Fort Worth airport, Lambert–St. Louis International Airport, Cincinnati Municipal Lunken Airport to change pilots and avoid strong winds, and Washington Dulles International Airport. On 6 July 2013, following a lengthy layover in Washington, Solar Impulse completed its cross-country journey, landing at New York City's JFK International Airport at 23:09 EDT. The landing occurred three hours earlier than originally intended, because a planned flyby of the Statue of Liberty was cancelled as a result of damage to the covering on the left wing.
Each flight leg took between 14 and 22 hours. The aircraft's second leg of its trip on 23 May to Dallas-Fort Worth covered and set several new world distance records in solar aviation.; ; ; ; and Solar Impulse 1 was placed on public display at JFK after its landing. In August 2013, it was disassembled, then transported via a Cargolux B-747-400F to Dübendorf Air Base, where it was placed in storage in a hangar.
Detailed route Source: Leg StartAll start times are given as UTC, and all start dates are 2013. Stop Origin Destination Distance Flight time Avg. speed Pilot 1 3 May 14:12 4 May 08:30 Moffett Field, California (KNUQ) Phoenix, Arizona (KGYR) 984 km 18 h 18 min 53 km/h Bertrand Piccard 2 22 May 12:47 23 May 07:08 Phoenix, Arizona (KGYR) Dallas, Texas (KDFW) 1541 km 18 h 21 min 84 km/h André Borschberg 3 3 Jun 10:06 4 Jun 07:28 Dallas, Texas (KDFW) Saint Louis, Missouri (KSTL) 1040 km 21 h 22 min 49 km/h Bertrand Piccard 4 14 Jun 11:01 15 Jun 02:15 Saint Louis, Missouri (KSTL) Cincinnati, Ohio (KLUK) 15 h 14 min André Borschberg 5 15 Jun 15:10 16 Jun 05:15 Cincinnati, Ohio (KLUK) Washington, DC (KIAD) 14 h 5 min Bertrand Piccard 6 6 July 09:56 7 July 05:15 Washington, DC (KIAD) New York City, New York (KJFK) 19 h 19 min André Borschberg
Aircraft on display
In March 2015, the plane was transported by truck to Paris to be part of the permanent exhibition at .
Solar Impulse 2 (HB-SIB)
Construction history Construction started in 2011 on the second aircraft, known as Solar Impulse 2, which carries the Swiss registration HB-SIB. Completion was initially planned for 2013, with a 25-day circumnavigation of the globe planned for 2014. A structural failure occurred on the aircraft's main spar during static tests in July 2012, leading to delays in the flight testing schedule to allow repairs. Solar Impulse 2s first flight took place at Payerne Air Base on 2 June 2014.
Design