Solar Aviation Technology

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.

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, 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. By February 2023, Sky dweller Aero had conducted its first autonomous flight and was planning to have a production aircraft operational by 2024; its goal is to operate year-round in latitudes between Miami (26°N) to Rio de Janeiro (23°S).

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 Borsch erg 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.  It continued across the US until it reached
New York City in June 2016. Later that month, the aircraft crossed the
Atlantic Ocean to the city of Seville.  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.

Project development and funding.

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 SASolvaySchindlerABB[25] and Peter Diamandis.  The EPFL, the European Space Agency and Dassault have provided technical expertise, while SunPower provided the aircraft’s photovoltaic cells.

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.

Specifications

Data from Solar Impulse Project  and Diaz

General characteristics

  • Crew: 1
  • Length: 21.85 m (71 ft 8 in)
  • Wingspan: 63.4 m (208 ft 0 in)
  • Height: 6.40 m (21 ft 0 in)
  • Wing area: 200 m2 (2,200 sq ft) covered with 11,628 photovoltaic cells rated at 45 kW peak
  • Aspect ratio: 19.7
  • Gross weight: 1,600 kg (3,500 lb)
  • Max takeoff weight: 2,000 kg (4,400 lb)
  • Fuel capacity: 21 kW⋅h (76 MJ) lithium-ion battery
  • Take-off speed: 35 km/h (22 mph)
  • Power plant: 4 × 7.5 kW (10 hp) electric motors
  • Propellers: 2-bladed, 3.5 m (11 ft 0 in) diameter

Performance

  • Cruise speed: 70 km/h (43 mph, 38 kn)
  • Endurance: approximately 36 hours
  • Service ceiling: 8,500 m (27,900 ft) with a maximum altitude of 12,000 m (39,000 ft)

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 8,700 m (28,500 ft).  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 international 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 1,800 m (6,000 ft) for a distance of 630 km (391 mi), with an average speed of 50 km/h (31 mph). 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.”

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 (1,099.3 km or 683 mi) and along a course (1,116 km or 693 mi).

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 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.

Detailed route

Source:[62]

Leg Start 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 Cité des Sciences et de l’Industrie.

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 2′s first flight took place at Payerne Air Base on 2 June 2014.

Design

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, but compared with the 500-ton A380, the carbon-fibre Solar Impulse weighs only about 2.3 tonnes (5,100 lb), little more than an average SUV.  It features a non-pressurized cockpit 3.8 cubic metres (130 cu ft) in size and advanced avionics, including limited functionality of an autopilot that allows the pilot to sleep for up to 20 minutes at a time, enabling multi-day transcontinental and trans-oceanic flights. Supplemental oxygen and various other environmental support systems allow the pilot to cruise up to an altitude of 12,000 metres (39,000 ft).

General characteristics

  • Crew: 1
  • Length: 22.4 m
    (73 ft 6 in)
  • Wingspan: 71.9 m
    (236 ft 0 in)
  • Height: 6.37 m
    (20 ft 11 in)
  • Gross
    weight:
     2,300 kg
    (5,100 lb)
  • Take-off
    speed:
     36 km/h
    (22.4 mph)
  • Wing
    area:
     17,248 photovoltaic solar cells cover the top of
    the wings, fuselage and tail plane for a total area of 269.5 m2 (2,901 sq ft)
    (rated at 66 kW peak)
  • Power
    plant:
     4
    × electric motors with 4 x 41 kW⋅h (150 MJ) lithium-ion batteries (633 kg or 1,396 lb), providing
    , 13.0 kW (17.4 hp) each [32]
  • Propellers: 4.0 m
    (13 ft 1 in) diameter

Performance

  • Maximum
    speed:
     140 km/h
    (87 mph, 76 kn)
  • Cruise
    speed:
     90 km/h
    (56 mph, 49 kn) 60 km/h (37 mph) at night to save power
  • Service
    ceiling:
     8,500 m
    (27,900 ft) with a maximum altitude of 12,000 m (39,000 ft)

By the end of May 2015, the plane had traversed Asia. It made
an unscheduled stop in Japan to await favorable weather over the Pacific,
increasing the expected number of legs of the journey to 13.  The aircraft began the flight from Japan to
Hawaii on 28 June 2015 (29 June, Japan local time).  With Borsch erg 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. The US Department of Transportation stored the aircraft in a
hangar at Kalaeloa Airport on Oahu.  New
batteries were made and installed in the plane. Test flights began in February
2016  to prepare for resumption of the
circumnavigation once northern hemisphere days lengthened enough to permit
multi-day solar-powered flights.  A favorable
weather window opened in April 2016, and the plane resumed its journey,  landing at Moffett Field, in California, on
23 April.  During that flight, Piccard,
via a live video link, spoke with Ban Ki-Moon and Doris Leuthard before the
General Assembly of the United Nations, from the cockpit of Solar Impulse 2,
commenting on that day’s historic signing of the Paris Agreement and discussing
how using clean technologies can create jobs and fight global warming.  Additional legs of the flight were added in
the US as Solar Impulse 2 flew to Phoenix, Arizona,  Tulsa, Oklahoma,  Dayton, Ohio,
Lehigh Valley, Pennsylvania[ and New York City, arriving there on 11
June 2016. The aircraft next stopped in Cairo, Egypt, on 13 July, and landed in
Abu Dhabi on 26 July, completing the around-the-world trip in a total of 17
stages and 16-1/2 months.

Post-Flight
Sale

In September 2019 the Solar Impulse 2 aircraft was sold to Sky dweller, a Spanish-American company that is developing autonomous unmanned aerial vehicles capable of continuous flight and “carrying radar, electronic optics, telecommunications devices, telephone listening and interception systems”. As part of this sale, the Solar Impulse 2 aircraft was transferred from Switzerland to Spain though once Sky dweller completes its research and development flights the Solar Impulse 2 will be transferred back to Switzerland for permanent display at the Swiss Museum of Transport.

History of Solar Aviation

During the 1970s fuel crisis, solar energy via photovoltaic panels was identified as an alternative energy source for humanity. Solar-powered airplanes have lately piqued the curiosity of the general public and the aviation industry due to their usage as an environmentally friendly alternative. Sunrise, the world’s first solar-powered airplane, took to the skies in 1974. 

They can cruise perpetually for an extended period, even
years, depending on the airplane system’s durability and sunshine circumstances,
something conventional airplanes cannot achieve owing to their operational
limitations.

Working Mechanisms

A circuit with a configurable microprocessor handles the power transmission output. The electricity regulation and transmission mechanism guarantee maximum energy output by the solar panels. The electricity generated is mostly used for propelling the aircraft and onboard electronics. The excess energy is utilized to recharge the batteries which are used in the absence of low sunlight.

Technological developments are being rapidly made to enhance and widen the applicability of solar aviation. Organic photovoltaic and quantum dots are essential in this regard. Organic photovoltaic (OPVs) are manufactured from organic materials that are varied and adaptable, providing limitless opportunities to improve a wide variety of features. Organic molecules are inexpensive; they have an excellent light absorption capability, allowing coatings as thin as several hundred nm to be used for this purpose.

Quantum dots have the potential to improve the efficiency of solar cells conversion in at least two ways: by expanding the energy gap of solar panels to collect more sunlight in the spectral region, and by producing more voltage from a single solar particle. Solar cells built on quantum dots could potentially transform more than 65% percent of the sun’s energy into electrical energy, increasing the efficiency by almost two times.

Nanomaterial’s are also considered to be essential in this regard. Nanomaterials like nanowires and nanoparticles offer novel potential in solar devices. Nano meter-sized objects have very high surface areas per unit volume, allowing for the formation of very large interfacial regions.

In short, ever since the first solar-powered air flight in
1974, the solar-powered aviation industry is being developed to meet the cost
and energy demands while maximizing the aerodynamic efficiency to perform
missions efficiently. Photovoltaic aircraft fly at higher elevations for long
periods, but with relatively limited applications, such as a tiny wing loading
for cargo. Subsystems such as energy, aerodynamics, propulsive systems, and
control mechanisms should be thoroughly researched to improve their performance
and broaden their range of applications.

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