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Solar Impulse

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Solar Impulse

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

Solar Impulse is 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 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.[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 aircraft are single-seat monoplanes powered by photovoltaic cells and 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.[3] 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.[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]

A second aircraft, completed in 2014 and named Solar Impulse 2, carries more solar cells and more powerful motors, among other improvements. In March 2015, Piccard and Borschberg began an attempt to circumnavigate the globe with Solar Impulse 2, departing from Abu Dhabi in the United Arab Emirates.[8] The aircraft was scheduled to return to Abu Dhabi in August 2015, upon the completion of its multi-stage journey.[9] By 1 June 2015, the plane had traversed Asia.[10] On 3 July 2015, the plane completed the longest leg of its journey, from Japan to Hawaii.[11] During that leg, however, the aircraft's batteries experienced thermal damage that is expected to take months to repair. The Solar Impulse team stated that they hope to resume the circumnavigation in April 2016.[12]

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.[13] 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.[14][15] The project is financed by a number of private companies and individuals, as well as receiving around CHF6 million (US$6.4 million) in funding from the Swiss government.[16]

The project's private financial backers include Omega SA, Solvay, Schindler, ABB[17] and Peter Diamandis.[18] The EPFL, the European Space Agency and Dassault have provided technical expertise, while SunPower provided the aircraft's photovoltaic cells.[19][20]

In July 2015, Piccard stated that the entire project from its beginnings in 2003 had cost €150 million, and that he hoped to raise an additional €20 million to continue the round-the-world flight from Hawaii.[21]


  • 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[22]
  • 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
  • 2015–2016: Circumnavigation of the Earth by Solar Impulse 2, conducted in twelve stages over two years[23][12][24]

Solar Impulse 1 (HB-SIA)

Solar Impulse 1 – fuselage and motors
Solar Impulse 1 – 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.[25] 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.[26][27]

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.[25] 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.[28]


Data from Solar Impulse Project[25] and Diaz[29]

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

Maiden flight and other early flights

Solar Impulse 1 during its first "flea hop" test flight in Dübendorf on 3 December 2009

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,[30] piloted by Markus Scherdel.[31] 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."[31]

On 7 April 2010, the plane conducted an 87-minute test flight, piloted by Markus Scherdel. This flight reached an altitude of 1,200 m (3,937 ft).[32][33] On 28 May 2010, the aircraft made its first flight powered entirely by solar energy, charging its batteries in flight.[34]

First overnight flight

On 8 July 2010, Solar Impulse 1 achieved the world's first manned 26-hour solar-powered flight.[35][36][37] 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.[38] During the flight, the plane reached a maximum altitude of 8,700 m (28,500 ft).[39] 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.[40][41]

International and intranational flights

Belgium and France (2011)
Solar Impulse 1 at Brussels Airport in May 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 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.[42] 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."[43][44]

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.[45] 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.[46]

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.[5] 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 (1,099.3 km (683 mi)) and along a course (1,116 km (693 mi)).[47]

United States (2013)
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.[48]

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.[49][50][51][52][53] On 4 June, the plane landed in St. Louis, Missouri.[54] It departed for Washington DC on 14 June, stopping overnight in Cincinnati, Ohio, to change pilots and avoid strong winds.[55] On 16 June, the plane landed at Washington Dulles International Airport in Virginia.[56] 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][57] 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] Solar Impulse 1 was placed on public display at JFK after its landing. In August 2013, it was disassembled and transported to Dübendorf Air Base where it was placed in storage in a hangar.

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 84 km/h 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)

Solar Impulse 2 at the Payerne Air Base in November 2014

Construction history

Construction of the second aircraft, known as Solar Impulse 2 and 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. Solar Impulse 2's first flight occurred at Payerne Air Base on 2 June 2014.[59]


The wingspan of Solar Impulse 2 is 71.9 m (236 ft), slightly less than that of an Airbus A380, the world's largest passenger airliner,[29] 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 non-pressurized cockpit 3.8 cubic meters in size[60] and advanced avionics, including an autopilot to allow for multi-day transcontinental and trans-oceanic flights.[14] Supplemental oxygen and various other environmental support systems allow the pilot to cruise up to an altitude of 12,000 metres (39,000 ft).[29]


Data from Solar Impulse Project[15]

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[22], electric motors (17.4 HP) each
  • Propeller diameter: 4 m (13.1 ft)
  • Take-off speed: 20 kn (36 km/h)


  • Maximum speed: 77 kn (140 km/h) 87 mph
  • Cruise speed: 49 kn (90 km/h) (33 kn (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

Flight suits worn on Solar Impulse

Solar Impulse 2 was first publicly displayed on 9 April 2014.[15] Its inaugural flight took place on 2 June 2014, piloted by Markus Scherdel.[61] The aircraft averaged a ground speed of 30 knots, and reached an altitude of 5,500 feet.[62] 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 (2015–16)

Due to the repair work to the aircraft's main spar, Solar Impulse 2's circumnavigation of the Earth was delayed from 2012 to 2015.[63] The aircraft was delivered to Masdar in Abu Dhabi for the World Future Energy Summit in late January 2015,[64] and it began the journey on 9 March 2015.[8][65] It was scheduled to return to the same location in August 2015.[9][66] 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 and the support team.[67]

The route to be followed by Solar Impulse 2 is entirely in the northern hemisphere; its closest approach to the equator was expected to be a flyby of Honolulu at 21.3° N.[66] Twelve stops were originally planned to allow the alternation and rest periods of pilots Borschberg and Piccard, and to ensure good weather conditions for each take-off and landing site along the route.[68] For most of its time airborne, Solar Impulse 2 is cruising at a ground speed of between 50 and 100 kilometers per hour – usually at the slower end of that range at night to save power. 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.[9][23] On multi-day flights, the pilots take 20-minute naps and use Yoga or other exercises to promote blood flow and maintain alertness.[60]

By the end of May 2015, the plane had traversed Asia.[69] It made an unscheduled stop in Japan to await favourable weather over the Pacific, increasing the expected number of legs of the journey to 13.[10][70] The aircraft began the flight from Japan to Hawaii on 28 June 2015 (29 June, Japan local time).[71] With Borschberg in the cockpit, it reached Hawaii on 3 July, setting new records for the world's longest solar-powered flight both by time (117 hours, 52 minutes) and distance (7,212 km; 4,481 mi). The flight's duration was also a record for longest solo flight, by time, for any aircraft.[11][72][73] During that leg, however, the plane's batteries were damaged by overheating caused by being packed in too much insulation. New parts are being ordered and, once installed, will need to be tested before long flights can resume. Therefore, Solar Impulse 2 is expected to remain in Hawaii until April 2016, when northern hemisphere days lengthen enough to permit multi-day solar-powered flights. In the meantime, the University of Hawaii and the US Department of Transportation are storing the aircraft in a hangar at Kalaeloa Airport on Oahu.[12][24]

Detailed route

Leg Start[75] Origin Destination Flight time Distance Avg. speed Max. altitude Pilot
1 9 March 03:12 Abu Dhabi, UAE (OMAD) Muscat, Oman (OOMS) 13 hrs 1 min 238 nmi (441 km) 18.3 kn (33.9 km/h) 20,942 ft (6,383 m) A. Borschberg[76]
2 10 Mar. 02:35 Muscat, Oman (OOMS) Ahmedabad, India (VAAH) 15 hrs 20 mins 802 nmi (1,485 km)[77] 52.3 kn (96.8 km/h) 29,114 ft (8,874 m) B. Piccard[78]
3 18 Mar. 01:48 Ahmedabad, India (VAAH) Varanasi, India (VIBN) 13 hrs 15 mins 656 nmi (1,215 km) 49.5 kn (91.7 km/h) 17,001 ft (5,182 m) Borschberg[79]
4 18 Mar. 23:52 Varanasi, India (VIBN) Mandalay, Myanmar (VYMD) 13 hrs 29 mins 755 nmi (1,398 km) 56.0 kn (103.7 km/h) 27,000 ft (8,230 m) Piccard[80]
5 29 Mar. 21:06 Mandalay, Myanmar (VYMD) Chongqing, China (ZUCK) 20 hrs 29 mins 788 nmi (1,459 km) 38.4 kn (71.2 km/h) 28,327 ft (8,634 m) Piccard[81]
6 20 April 22:06 Chongqing, China (ZUCK) Nanjing, China (ZSNJ) 17 hrs 22 mins 726 nmi (1,344 km) 41.8 kn (77.4 km/h) 14,010 ft (4,270 m) Piccard[82]
7 30 May 18:39 Nanjing, China (ZSNJ) Nagoya, Japan (RJNA) 44 hrs 10 mins[83] 1,540 nmi (2,852 km)[84] 34.9 kn (64.6 km/h) 28,000 ft (8,500 m) Borschberg[10][84]
8 28 June 18:03 Nagoya, Japan (RJNA) Kalaeloa, Hawaii, USA (PHJR) 117 hrs 52 mins[85] 3,894 nmi (7,212 km)[72] 33.04 kn (61.19 km/h) 28,327 ft (8,634 m) Borschberg[72][86]
9 Kalaeloa, Hawaii, USA (PHJR) Phoenix, AZ, USA (KPHX) 100 hrs (planned) 2,542 nmi (4,707 km) (planned) [87]
10 Phoenix, AZ, USA TBD (mid-USA) 30 hrs (planned) 1,100 nmi (2,030 km) (planned) [88]
11 TBD (mid-USA) New York, USA 20 hrs (planned) 775 nmi (1,436 km) (planned) [89]
12 New York, USA TBD (Southern Europe or Morocco) 120 hrs (planned) 3,099 nmi (5,739 km) (planned) [90]
13 TBD (Southern Europe or Morocco) Abu Dhabi, UAE 120 hrs (planned) 3,156 nmi (5,845 km) (planned) [91]


See also


  1. ^ a b
  2. ^
  3. ^
  4. ^ "Swiss solar plane makes history with night flight". Swisster. 8 July 2010. Retrieved 13 July 2010.
  5. ^ a b
  6. ^ a b c
  7. ^ a b c d
  8. ^ a b
  9. ^ a b c
  10. ^ a b c d "Leg 7 of 13 – Nanjing, China to Nagoya, Japan", Solar Impulse, accessed 29 July 2015; "Solar Impulse touches down on unscheduled Japan stop", The Sun Daily (Malaysia), 2 June 2015
  11. ^ a b Archangel, Amber. "Solar Impulse Sets World Record: 117 Hours & 52 Minutes – Longest Solo Flight Ever",, 6 July 2015
  12. ^ a b c Amos, Jonathan. "Solar Impulse grounded until 2016", BBC, 15 July 2015
  13. ^
  14. ^ a b
  15. ^ a b c "Building a Solar Airplane". Solar Impulse. Retrieved 19 January 2015.
  16. ^
  17. ^
  18. ^
  19. ^ ; and
  20. ^
  21. ^
  22. ^ a b
  23. ^ a b
  24. ^ a b Molko, Davis. "Solar Impulse: Plane's pilots ground record-setting attempt until 2016", CNN, July 15, 2015
  25. ^ a b c
  26. ^
  27. ^
  28. ^
  29. ^ a b c
  30. ^
  31. ^ a b
  32. ^
  33. ^
  34. ^
  35. ^
  36. ^
  37. ^
  38. ^
  39. ^
  40. ^
  41. ^
  42. ^
  43. ^
  44. ^
  45. ^
  46. ^
  47. ^ Solar Impulse’s HB-SIA obtains two new world records. 26 September 2012. See also: FAI Record ID #16558 and FAI Record ID #16560.
  48. ^
  49. ^
  50. ^
  51. ^
  52. ^
  53. ^
  54. ^
  55. ^
  56. ^
  57. ^
  58. ^
  59. ^
  60. ^ a b Reisinger, Don. "Solar-powered plane embarks on longest leg of round-the-world flight",, June 29, 2015
  61. ^
  62. ^
  63. ^ Timeline: "Without a spar, what's next?" Solar Impulse. 19 July 2012. Retrieved 28 June 2013.
  64. ^
  65. ^ a b
  66. ^ a b
  67. ^
  68. ^ Molko, David. "Solar-powered plane on round-the-world flight gets stuck in China", CNN, April 17, 2015
  69. ^ Amos, Jonathan. "Solar Impulse plane begins Pacific crossing", BBC News, May 31, 2015
  70. ^ Randall, Tom. "This Plane Runs on Sun and Is About to Smash Some Records",, June 15, 2015
  71. ^ Morelle, Rebecca. "Solar Impulse begins second bid to cross Pacific Ocean", BBC News, 28 June 2015
  72. ^ a b c The Fédération Aéronautique Internationale (FAI) website states that the "Free distance along course" was 7,039.9 km. FAI Record ID #17595, Fédération Aéronautique Internationale, accessed 29 July 2015
  73. ^ The FAI does not record this record as official, since the FAI does not have an "any aircraft" category. See "FAI records page", Fédération Aéronautique Internationale, 29 July 2015
  74. ^
  75. ^ All start times are given as UTC, and all start dates are 2015.
  76. ^
  77. ^ The FAI website states that the record "Straight Distance - pre-declared waypoints" was 1468 km. FAI "Record ID #17429", Fédération Aéronautique Internationale, accessed 1 August 2015
  78. ^
  79. ^
  80. ^
  81. ^
  82. ^
  83. ^ "FAI Record ID #17557", Fédération Aéronautique Internationale, accessed 29 July 2015
  84. ^ a b The FAI website states that the "Free distance along course" was 2614.5 km. FAI "Record ID #17558", Fédération Aéronautique Internationale, accessed 29 July 2015
  85. ^ "FAI Record ID #17594", Fédération Aéronautique Internationale, accessed 29 July 2015
  86. ^ "Leg 8 of 13 – Nagoya, Japan to Hawaii, USA", Solar Impulse, accessed 29 July 2015
  87. ^
  88. ^ a b
  89. ^
  90. ^
  91. ^

External links

  • Official website and YouTube channel
  • "Bertrand Piccard's solar-powered adventure" – lecture at TED (17 min). July 2009
  • "Solar-powered plane aims to fly around the world". 60 Minutes. CBS News. December 2012
  • "How does Solar Impulse work?" How It Works. 13 May 2011
  • "Record-attempting solar powered plane's first 'hop'". BBC. 4 December 2009
  • "Solar Impulse plane starts 24-hour test flight" . BBC. 7 July 2010
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