Solar Impulse

Solar Impulse is a pioneering aviation project that successfully demonstrated the potential of solar energy for long-duration, fuel-free flight. Conceived and led by Swiss explorer Bertrand Piccard and engineer André Borschberg, the initiative produced two experimental aircraft—Solar Impulse 1 (HB-SIA) and Solar Impulse 2 (HB-SIB)—designed to fly powered entirely by solar energy. The project became a global symbol of technological innovation, environmental sustainability, and the possibilities of renewable energy in transportation.

Origins and Concept

The idea for Solar Impulse emerged in the early 2000s, inspired by advances in renewable technology and the growing urgency to address climate change. Bertrand Piccard, who had previously completed the first non-stop balloon flight around the world in 1999, envisioned creating an aircraft that could circumnavigate the globe using only solar power.
With the collaboration of EPFL (École Polytechnique Fédérale de Lausanne) as the project’s official scientific partner, research began in 2003. The goal was to design an aircraft with maximum energy efficiency—lightweight, aerodynamically optimised, and capable of flying both day and night without fossil fuels.
The project officially launched in 2004, supported by a consortium of scientific institutions, industrial partners, and sponsors including Solvay, Omega, ABB, and Swisscom.

Design and Technical Features

The Solar Impulse aircraft were built using advanced materials and engineering techniques to achieve the delicate balance between weight, strength, and energy capacity required for sustained solar flight.
Key design features included:

• Wingspan: Solar Impulse 2 had a wingspan of 72 metres, larger than that of a Boeing 747, yet weighed only 2,300 kilograms, roughly equivalent to an average car.
• Solar Cells: Approximately 17,000 photovoltaic cells were mounted on the wings and fuselage, converting sunlight into electricity.
• Energy Storage: Four high-density lithium polymer batteries stored energy for night flying, accounting for nearly a quarter of the aircraft’s total weight.
• Engines: Four electric motors, each delivering about 17.5 horsepower (13.5 kW), powered large, slow-turning propellers for efficient thrust.
• Cruising Speed: The aircraft flew at an average speed of 45–90 km/h, depending on sunlight intensity and altitude.
• Altitude: It could climb up to 8,500 metres (28,000 feet) during the day to capture solar energy and descend at night to conserve power.

The entire system was designed for maximum energy efficiency, with ultra-light carbon-fibre composites and precise aerodynamic control.

Solar Impulse 1 (HB-SIA)

Solar Impulse 1, the prototype aircraft, was completed in 2009 and made its maiden flight in 2009 at Dübendorf Air Base, Switzerland. Its key milestone occurred in July 2010, when it achieved the first 26-hour solar-powered flight, proving that solar energy collected during the day could sustain night flight without fuel.
Subsequent test flights in Europe and North Africa further validated the concept. In 2012, Solar Impulse 1 completed a successful flight from Switzerland to Morocco, covering 2,500 km and demonstrating the feasibility of intercontinental solar aviation.

Solar Impulse 2 (HB-SIB)

Building on the success of its predecessor, Solar Impulse 2 was unveiled in 2014 as the aircraft designed for global circumnavigation. It featured improved aerodynamics, enhanced battery capacity, and a more spacious single-seat cockpit equipped for long-duration missions.
The aircraft’s flight controls and systems were optimised for efficiency, while the cockpit was designed to support pilots on multi-day missions with reclining seats, oxygen supplies, and satellite communication systems.

The Round-the-World Flight (2015–2016)

Solar Impulse 2 embarked on its historic global flight on 9 March 2015, departing from Abu Dhabi, United Arab Emirates, with the mission to demonstrate that clean technologies can achieve the seemingly impossible.
The journey included multiple legs across Asia, the Pacific, North America, the Atlantic, and Europe before returning to its starting point. Key milestones included:

• Abu Dhabi to Muscat (Oman) – The first leg, testing performance in desert conditions.
• Across India and Myanmar – Promoting renewable energy awareness across densely populated regions.
• Nagoya to Hawaii (June–July 2015) – A record-breaking 8,924 km flight lasting nearly five days, the longest solo flight in aviation history at that time.
• Hawaii to California (2016) – After a forced pause for battery repairs, the aircraft resumed its journey, completing the first solar flight across the Pacific Ocean.
• Crossing the United States and Atlantic – Reached New York, then Spain, and finally returned to Abu Dhabi on 26 July 2016, completing the first fuel-free circumnavigation of the Earth.

The global flight covered over 42,000 kilometres in 17 separate legs, taking approximately 505 hours of flight time.

Objectives and Scientific Significance

Solar Impulse was not intended to revolutionise commercial aviation but to showcase the potential of renewable energy technologies. The project’s goals included:

• Demonstrating the feasibility of solar power for long-duration operations.
• Encouraging innovation in energy efficiency and battery technology.
• Inspiring sustainable approaches across industries beyond aviation.
• Promoting global awareness about climate change and clean energy transitions.

It served as a mobile laboratory, testing cutting-edge materials, control systems, and solar technologies that have potential applications in electric mobility, renewable energy storage, and lightweight engineering.

Achievements and Records

Solar Impulse achieved several world records and milestones, including:

• The first night flight powered solely by solar energy (2010).
• The longest solo flight in aviation history (Nagoya–Hawaii leg, 2015).
• The first solar-powered aircraft to circumnavigate the globe (2016).
• Demonstrated that solar and battery technology could sustain flight without fuel.

The project’s technical innovations contributed to advances in energy storage, photovoltaic efficiency, and lightweight materials, inspiring applications in both aerospace and renewable energy sectors.

Legacy and Impact

The completion of Solar Impulse 2’s world flight marked a milestone in human ingenuity and environmental advocacy. It transformed perceptions of clean energy, showing that technologies available today can power extraordinary achievements.
Following the project, Bertrand Piccard and André Borschberg founded the Solar Impulse Foundation, dedicated to identifying and supporting 1,000 efficient and profitable solutions for environmental sustainability. The foundation continues to collaborate with governments, companies, and innovators to accelerate the adoption of clean technologies.
Solar Impulse has also influenced subsequent developments in electric and hybrid aviation, inspiring companies and researchers to pursue sustainable alternatives in aerospace design.