Solar Impulse

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Solar Impulse
SolarImpulse HB-SIA landing Brussels Airport 3-crop.jpg
Solar Impulse 1 (HB-SIA) landing at Brussels Airport after its first international flight on 13 May 2011.
Role Experimental solar-powered aircraft
National origin Swiss
Manufacturer Solar Impulse
Designer Solar Impulse
First flight 3 December 2009
Number built 2 (including prototype)

Solar Impulse is the name of a Swiss long-range experimental solar-powered aircraft project, and also the name of the project's two operational aircraft.[1] The privately-financed project is led by Swiss businessman André Borschberg and Swiss psychiatrist and aeronaut Bertrand Piccard, who co-piloted the first balloon to circle the world non-stop.[2] The Solar Impulse project intends to achieve the first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power.

The prototype aircraft, bearing the Swiss aircraft registration code HB-SIA and often referred to as Solar Impulse 1, is a single-seat monoplane powered by photovoltaic cells and capable of taking off under its own power. It is designed to remain airborne up to 36 hours.[3] The aircraft 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.[4] Piccard and Borschberg completed successful solar-powered flights from Switzerland to Spain and then Morocco in 2012,[5] and conducted a multi-stage flight across the United States in 2013.[6][7]

Improving on the prototype, a slightly larger design was created in 2014, designated HB-SIB and named Solar Impulse 2. In March 2015, Piccard and Borschberg began a circumnavigation of the globe with Solar Impulse 2, departing from Abu Dhabi in the United Arab Emirates.[8] The aircraft is scheduled to return to Abu Dhabi in August 2015.[9]

Design and development[edit]

Bertrand Piccard initiated the Solar Impulse project in November 2003 after undertaking a feasibility study in partnership with the Ecole Polytechnique Fédérale de Lausanne.[10] By 2009, he 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.[11][12] The project is financed by a number of private companies and individuals. The first company to officially support the project was Semper Gestion, after its co-founder Eric Freymond was convinced of the future success of Piccard.[13] The project's primary partners are Omega SA, Solvay, Schindler and ABB.[14] Other partners and supporters of the project include Bayer MaterialScience, Altran, Swisscom, Swiss Re (Corporate Solutions), Clarins, Toyota, BKW FMB Energie and Symphony Technology Group. The EPFL, the European Space Agency (ESA) and Dassault have provided additional technical expertise, while SunPower provided the aircraft's photovoltaic cells.[15][16] Additionally, the Swiss Government has provided six million Euros of support.[17]

In October 2013, Solar Impulse announced that Peter Diamandis, founder of the X Prize Foundation, had become a supporter of the project after meeting with Solar Impulse officials during Google's 2013 Zeitgeist event.[18]


  • 2003: 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[19]
  • 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 (Mission Across America)[1][6][7]
  • 2014: First flight of Solar Impulse 2
  • 2015: Circumnavigation by Solar Impulse 2, conducted in twelve stages over five months[8][11][20]

Solar Impulse 1 (HB-SIA)[edit]

Image of HB-SIA showing fuselage and engines.
Image of HB-SIA showing wing structure.

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 10 hp (7.5 kW) electric motor and one twin-bladed propeller. To keep the wing as light as possible, a customised carbon fibre honeycomb sandwich structure was used.[21] 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.[22][23]

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 8 hp (6 kW), roughly the power used by the Wright brothers' Flyer, the first successful powered aircraft, in 1903.[21] 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.[24]


Data from Solar Impulse Project[21] and Diaz[25]

General characteristics

  • Crew: 1
  • Length: 21.85 m (71.7 ft)
  • Wingspan: 63.4 m (208 ft)
  • Height: 6.40 m (21.0 ft)
  • Wing area: 11,628 photovoltaic cells rated at 45 kW peak: 200 m2 (2,200 sq ft)
  • Aspect ratio: 19.7
  • Loaded weight: 1,600 kg (3,500 lb)
  • Max. takeoff weight: 2,000 kg (4,400 lb)
  • Powerplant: 4 × electric motors, 4 x 21 kWh lithium-ion batteries (450 kg), providing 7.5 kW (10 HP) each
  • Propeller diameter: 3.5 m at 200 to 400 rpm (11 ft)
  • Take-off speed: 35 kilometres per hour (22 mph)


Operational history[edit]

Maiden flight and other early flights[edit]

Solar Impulse 1 (HB-SIA) during its first "flea hop" test flight in Dübendorf on 3 December 2009

On 26 June 2009, the Solar Impulse 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,[26] piloted by Markus Scherdel.[27] André Borschberg, co-leader of the project team, said of the flight:

"It was an unbelievable day. The airplane flew for about 350 metres (1,150 ft) and about 1 metre (3 ft 3 in) above the ground ... The aim was not to get high but to land on the same runway at a speed to test its controllability and get a first feeling of its flying characteristics ... the craft behaved just as the engineers had hoped. It is the end of the engineering phase and the start of the flight testing phase."[27]

On 7 April 2010, the HB-SIA conducted an 87-minute test flight, piloted by Markus Scherdel. This flight reached an altitude of 1,200 m (3,937 ft).[28][29] On 28 May 2010, the aircraft made its first flight powered entirely by solar energy, charging its batteries in flight.[30]

First overnight flight[edit]

On 8 July 2010, the HB-SIA achieved the world's first manned 26-hour solar-powered flight.[31][32][33] The airplane was flown by André Borschberg, and took off at 6:51 a.m. Central European Summer Time (UTC+2) on 7 July from Payerne Air Base, Switzerland. It returned for a landing the following morning at 9:00 a.m. local time.[34] During the flight, the plane reached a maximum altitude of 8,700 m (28,500 ft).[35] 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.[36][37]

International and intranational flights[edit]

Belgium and France (2011)[edit]
Solar Impulse 1 at Brussels Airport in May 2011.

On 13 May 2011 at 21:30 local time, HB-SIA 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 6,000 ft (1,800 m) for a distance of 630 km (391 mi), with an average speed of 50 km/h (31 mph). The aircraft's slow cruising speed required operating at a mid-altitude, allowing much faster air traffic to be routed around it.[38] The aircraft was piloted by Andre Borschberg. The project's other co-founder, Bertrand Piccard, said in an interview after the landing: "Our goal is to create a revolution in the minds of promote solar energies – not necessarily a revolution in aviation."[39][40]

A second international flight to the Paris Air Show was attempted on 12 June 2011, but the plane turned back and returned to Brussels, due to adverse weather conditions.[41] In a second attempt on 14 June, André Borschberg successfully landed the aircraft at Paris' Le Bourget Airport at 9:15 pm after a 16-hour flight.[42]

First intercontinental flight (2012)[edit]

On 5 June 2012, the Solar Impulse successfully completed its first intercontinental flight, a 19-hour trip from Madrid, Spain, to Rabat, Morocco.[5] During the first leg of the flight from Payerne, Switzerland, to Madrid, the aircraft broke several further records for solar flight, including the longest solar-powered flight between pre-declared waypoints (1,099.3 km (683 mi)) and along a course (1,116 km (693 mi)).[43]

United States (2013)[edit]
Solar Impulse 1 on display at John F. Kennedy International Airport, New York, on 14 July 2013.

On 3 May 2013, the plane began its cross-US flight with a journey from Moffett Field in Mountain View, California, to Phoenix Sky Harbor International Airport in Arizona. Successive legs of the flight took the Solar Impulse to Dallas-Fort Worth airport, Lambert–St. Louis International Airport, an overnight stop at Cincinnati Municipal Lunken Airport, and Washington Dulles International Airport; it concluded at New York's John F. Kennedy International Airport on 6 July. Each flight leg took between 19 and 25 hours, with multi-day stops in each city (except Cincinnati) between flights.[44]

After the first leg to Phoenix,[6] the aircraft completed the second leg of its trip on 23 May, landing at Dallas-Fort Worth International Airport. This flight, which covered 1,541 kilometres (958 mi), set several new world distance records in solar aviation.[45][46][47][48][49] On 4 June, the plane landed in St. Louis, Missouri.[50] It departed for Washington DC on 14 June, stopping overnight in Cincinnati, Ohio, to change pilots and avoid strong winds.[51] On 16 June, the plane landed at Washington Dulles International Airport in Virginia.[52] 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 11:09 p.m. EDT.[7][53] The landing occurred three hours earlier than originally intended, because a planned flyby of the Statue of Liberty was cancelled due to damage to the covering on the left wing.[7] The aircraft was placed on public display at JFK after its landing. HB-SIA was disassembled in the USA and brought back to Dübendorf Air Base (ICAO: LSMD) on 5 August 2013 by a Cargolux B747F. Thereafter, HB-SIA remained in storage in a hangar at Dübendorf AFB.

Detailed route


Leg Start Stop Origin Destination Distance Flight time Avg. speed Pilot
1  3 May 2013, 06:12 PDT (UTC-7)  4 May 2013, 00:30 MST (UTC-7) Moffett Field, California (KNUQ) Phoenix, Arizona (KPHX)  km 18 hrs 18 mins  km/h Bertrand Piccard
2 22 May 2013, 04:47 MST (UTC-7) 23 May 2013, 01:08 CDT (UTC-5) Phoenix, Arizona (KPHX) Dallas, Texas (KDFW) 1541 km 18 hrs 21 mins André Borschberg
3  3 Jun 2013, 04:06 CDT (UTC-5)  4 Jun 2013, 01:28 CDT (UTC-5) Dallas, Texas (KDFW) Saint Louis, Missouri (KSTL) 1040 km 21 hrs 22 mins 49 km/h Bertrand Piccard
4 14 Jun 2013, 05:01 CDT (UTC-5) 14 Jun 2013, 20:15 EDT (UTC-4) Saint Louis, Missouri (KSTL) Cincinnati, Ohio (KLUK) 15 hrs 14 mins André Borschberg
5 15 Jun 2013, 10:10 EDT (UTC-4) 16 Jun 2013, 00:15 EDT (UTC-4) Cincinnati, Ohio (KLUK) Washington, DC (KIAD) 14 hrs 5 mins Bertrand Piccard
6  6 July 2013, 04:56 EDT (UTC-4)  7 July 2013, 00:15 EDT (UTC-4) Washington, DC (KIAD) New York City, New York (KJFK) 19 hrs 19 mins André Borschberg

Solar Impulse 2 (HB-SIB)[edit]

Solar Impulse 2 (HB-SIB) at Payerne aerodrome in November 2014.

Construction history[edit]

Construction of the second Solar Impulse aircraft, carrying the Swiss registration HB-SIB, started in 2011. Completion was initially planned for 2013, with a 25-day circumnavigation of the globe planned for 2014. However, a structural failure of the aircraft's main spar occurred during static tests in July 2012, leading to delays in the flight testing schedule to allow for repairs. HB-SIB's first flight occurred at Payerne aerodrome on 2 June 2014.[55]


The wingspan of HB-SIB is 71.9 m (236 ft), slightly less than that of an Airbus A380, the world's largest passenger airliner,[25] but unlike the 500-ton A380, the carbon-fibre Solar Impulse weighs only 2.3 tonnes (5,100 lb), little more than an average automobile. It features a larger, non-pressurized cockpit and advanced avionics, including an autopilot to allow for multi-day transcontinental and trans-oceanic flights.[11] Supplemental oxygen and various other environmental support systems allow the pilot to cruise up to an altitude of 12,000 metres (39,000 ft).[25]


Data from Solar Impulse Project[12]

General characteristics

  • Crew: 1
  • Length: 22.4 m (73.5 ft)
  • Wingspan: 71.9 m (236 ft)
  • Height: 6.37 m (20.9 ft)
  • Wing area: 17,248 photovoltaic cells cover the top of the wings, fuselage and tailplane for a total area of 269.5 m2 (rated at 66 kW peak)
  • Loaded weight: 2,300 kg (5,100 lb)
  • Powerplant: 4 × electric motors powered from solar cells and 4 x 41 kWh lithium-ion batteries (633 kg), providing 13 kW[19], electric motors (17.4 HP) each
  • Propeller diameter: 4 m (13.1 ft)
  • Take-off speed: 20 kts (36 km/h)


  • Maximum speed: 77 kts (140 km/h) 87 mph
  • Cruise speed: 49 kts (90 km/h) (33 kts (60 km/h) at night to save power)
  • Service ceiling: 8,500 m (27,900 ft) with a maximum altitude of 12,000 metres (39,000 ft)

Operational history[edit]

HB-SIB was first publicly displayed on 9 April 2014.[12] Its inaugural flight took place on 2 June 2014, piloted by Markus Scherdel.[56] The aircraft averaged a ground speed of 30 knots, and reached an altitude of 5,500 feet.[57] The first night flight was completed on 26 October 2014, and the aircraft reached its maximum altitude during a flight on 28 October 2014.

Circumnavigation flight (2015)[edit]

Due to the repair work to the aircraft's main spar, Solar Impulse 2's circumnavigation of the Earth was rescheduled from 2012 to March 2015.[58] The aircraft was delivered to Masdar in Abu Dhabi for the World Future Energy Summit in late January 2015,[59] and it began the circumnavigation on 9 March 2015.[8][60] It is scheduled to return to the same location in August 2015.[9][61] A mission control centre for the circumnavigation was established in Monaco, utilizing satellite links to gather real-time flight telemetry and remain in constant contact with the aircraft.[62]

The aircraft is currently circling the world in the northern hemisphere; the closest it will get to the equator will be a flyby of Honolulu at 21.3° N.[61] Twelve stops are planned to allow the alternation of pilots Borschberg and Piccard. For most of its time airborne, Solar Impulse 2 is cruising at between 50 and 100 kilometers per hour – usually at the slower end of that range at night, in order to save power.[20] The legs of the flight crossing the Pacific and Atlantic oceans are the longest stages of the circumnavigation, and are each expected to take about five days, covering a distance of up to 8,500 kilometres (5,270 miles).[9][20]

Detailed route[edit]


Leg Start Origin Destination Distance Flight time Pilot
1 9 March 2015 03:12 UTC United Arab Emirates Abu Dhabi, UAE Oman Muscat, Oman 188 nmi (349 km) 13 hrs 1 min André Borschberg
2 10 March 2015 02:35 UTC Oman Muscat, Oman India Ahmedabad, India 793 nmi (1,468 km) 15 hrs 20 mins Bertrand Piccard
3 18 March 2015 01:48 UTC India Ahmedabad, India India Varanasi, India 578 nmi (1,071 km) 15 hrs 56 mins André Borschberg
4 18 March 2015 23:52 UTC India Varanasi, India Burma Mandalay, Myanmar 756 nmi (1,401 km) 13 hrs 29 mins Bertrand Piccard
5 29 March 2015 ~23:00 UTC Burma Mandalay, Myanmar China Chongqing, China 750 nmi (1,389 km)
6 China Chongqing, China China Nanjing, China
7 China Nanjing, China United States Hawaii, USA
8 United States Hawaii, USA United States Phoenix, USA
9 United States Phoenix, USA United States TBD (mid-USA)
10 United States TBD (mid-USA) United States New York, USA
11 United States New York, USA TBD (Southern Europe or Morocco)
12 TBD (Southern Europe or Morocco) United Arab Emirates Abu Dhabi, UAE

See also[edit]

Aircraft of comparable role, configuration and era


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External links[edit]