A revolutionary step in solar-powered aviation, Solar Impulse 2 (HB-SIB) represents the perfect balance between lightweight design, advanced batteries, and clean solar energy.
Vision and Development
Solar Impulse 2 was the creation of Swiss pioneers Bertrand Piccard and André Borschberg, whose goal was to demonstrate that renewable energy could achieve what fossil fuels had always dominated: long-distance, sustained flight.
Construction began in 2011 at Payerne Air Base in Switzerland. The engineering team designed every element of the aircraft to fly day and night powered only by sunlight. Every component was optimized for efficiency—lightweight materials, high-efficiency solar panels, and energy-dense lithium-ion batteries worked together to make perpetual flight possible.
After a series of structural challenges, including a spar failure in 2012, the team successfully launched Solar Impulse 2’s maiden flight on June 2, 2014. This marked the beginning of a project that would eventually lead to the first solar-powered flight around the world.
Lightweight Carbon Design
Solar Impulse 2’s carbon-fibre structure is one of the most remarkable achievements in modern aerospace design. Despite a wingspan of 71.9 meters—almost equal to an Airbus A380—the aircraft weighs only 2,300 kilograms, similar to a large SUV.
The design principle was clear: maximize lift, minimize weight. Every section of the fuselage and wings was made from ultra-light carbon composites, chosen for strength, flexibility, and minimal mass. Every bolt, wire, and surface was calculated to save energy and reduce drag.
This extreme lightness enabled the plane to maintain altitude at low speeds, using very little energy—an essential factor for an aircraft powered solely by sunlight.
Solar Power System
The upper surfaces of the wings, tailplane, and fuselage are covered with 17,248 photovoltaic cells, forming a total surface area of 269.5 square meters. These high-efficiency cells can produce up to 66 kilowatts of electrical power under ideal sunlight conditions.
During the day, the solar panels simultaneously powered the four electric motors and charged the lithium-ion batteries for night flight. Each of the four motors produced around 13 kilowatts (17.4 horsepower) and drove a 4-meter propeller. The overall propulsion system achieved over 90 percent efficiency, a level far beyond conventional combustion engines.
The result was a silent, emission-free flight capable of crossing continents and oceans.
Lithium-Ion Battery Innovation
At the heart of Solar Impulse 2 lies its lithium-ion battery system, weighing 633 kilograms—approximately one-quarter of the aircraft’s total weight. These batteries stored enough energy for up to ten hours of night flight, maintaining a steady cruising speed of 60 kilometers per hour after sunset.
Battery management proved to be one of the project’s greatest challenges. During early test flights, the team encountered overheating risks, particularly in tropical climates. Engineers developed a complex insulation and cooling system to maintain stable battery temperatures and prevent degradation.
These advances in battery management and thermal protection influenced subsequent generations of electric aircraft and ground-based energy systems.
Intelligent Flight and Pilot Endurance
The non-pressurized cockpit, measuring just 3.8 cubic meters, was designed for a single pilot. Despite its limited space, it contained advanced avionics and an autopilot system that allowed the pilot to sleep for 20-minute intervals while maintaining flight stability.
On multi-day transoceanic flights, the pilots practiced controlled rest, breathing techniques, and stretching exercises to remain alert. Supplemental oxygen and thermal protection systems made it possible to cruise up to 12,000 meters (39,000 feet).
These endurance missions demonstrated not only technological innovation but also human adaptability under extreme conditions.
Performance Specifications
| Specification | Detail |
|---|---|
| Wingspan | 71.9 m |
| Weight | 2,300 kg |
| Power | 4 × 13 kW electric motors |
| Solar Cells | 17,248 (269.5 m² total area) |
| Battery Capacity | 4 × 41 kWh lithium-ion (633 kg total) |
| Cruise Speed (Day/Night) | 90 / 60 km/h |
| Maximum Altitude | 12,000 m |
| Takeoff Speed | 36 km/h |
A Symbol of Sustainable Flight
Solar Impulse 2 proved that clean energy technologies are not limited to laboratory experiments—they can perform in one of the most demanding environments imaginable. The project became a living symbol of what can be achieved with solar power, battery innovation, and human determination.
Its historic 2016 circumnavigation—from Abu Dhabi, across Asia, the Pacific, the United States, the Atlantic, and back—marked a defining moment in the history of aviation.
Solar Impulse 2 demonstrated that renewable energy is not just a dream of the future—it is already capable of taking us around the world.
Reflection
Solar Impulse 2 stands as a reminder that engineering, creativity, and sustainability can coexist. It redefined what flight could mean in an era where energy efficiency and environmental responsibility are becoming essential.
How long will it take before commercial passenger aircraft follow its solar-powered example?