World’s Largest Solar-Powered Aircraft: “Solar Impulse”
The Solar Impulse project is a groundbreaking journey into the future of aviation. As the world’s largest solar-powered aircraft, Solar Impulse represents a significant leap toward sustainability and clean energy. The project was initiated with a bold vision: to create an aircraft capable of flying around the world using only solar energy. Swiss adventurer Bertrand Piccard and engineer André Borschberg launched the project in 2003 to showcase the potential of renewable energy in aviation. The result was Solar Impulse 2 (SI2), which completed a historic global circumnavigation. How does Solar Impulse achieve this remarkable feat? What distinguishes it from traditional fuel-powered aircraft? Let’s now explore the technology behind Solar Impulse.
How This Project Came Into Being
The Solar Impulse project began with the ambitious vision of Bertrand Piccard and André Borschberg. Their goal was to build an aircraft that could circumnavigate the globe using only solar power. Launched in 2003, the project aimed to push the boundaries of solar technology and challenge conventional ideas about air travel. By 2009, they 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.
In 2009, Solar Impulse 1, the prototype, made its maiden flight. However, it was Solar Impulse 2 (SI2) that achieved the monumental task of flying around the world. This milestone came after years of intense research and development. The team faced numerous challenges, including designing a lightweight yet durable structure and harnessing sufficient solar energy for extended flights.
“We had to create an airplane with the wingspan of a jumbo jet, yet the weight of a car.”
André Borschberg
Technology Behind Solar Impulse
The success of Solar Impulse hinges on its advanced technology. The aircraft’s wingspan spans 72 meters—similar to that of a Boeing 747—but it weighs only about 2,300 kilograms, roughly the weight of a car. This lightness is achieved through the use of lightweight materials such as carbon fiber, which forms the majority of the aircraft’s structure.
Solar Impulse is equipped with 17,248 solar cells covering its wings. These cells convert sunlight into electricity, which powers the plane’s four electric motors. Each motor generates about 17.5 horsepower, sufficient to keep the plane in the air despite being less powerful than traditional fuel-powered engines. The efficiency of these solar cells is critical for both daytime operation and nighttime flight, as they need to collect enough energy to power the aircraft during the night.
Differences Between Solar Impulse and Fuel-Powered Aircraft
Solar Impulse contrasts sharply with traditional fuel-powered aircraft. First and foremost, it is entirely emission-free. While conventional planes burn fossil fuels, releasing significant amounts of CO2 and other pollutants, Solar Impulse relies solely on clean solar energy.
Moreover, Solar Impulse’s lightweight design is in stark contrast to the heavy construction of most fuel-powered aircraft. The emphasis on minimizing weight is crucial for solar-powered flight, as the weight of the fuel alone in traditional aircraft can exceed the total weight of Solar Impulse. This focus on efficiency and lightness is vital for the aircraft’s performance.
Another notable difference is speed. Solar Impulse travels at a much slower pace—between 50 to 90 kilometers per hour—compared to conventional aircraft, which can exceed speeds of 900 kilometers per hour. This slower speed results from the lower energy output of solar power versus fuel-based engines. However, this reduced speed enables long-distance travel without burning fuel, albeit over extended periods.
Circumnavigation: The Historic Flight Around the World
In 2015, Solar Impulse 2 embarked on a groundbreaking journey to circumnavigate the globe. Starting in Abu Dhabi, the journey took over a year to complete, with the aircraft making stops in 17 cities across four continents. The flight over the Pacific and Atlantic Oceans showcased the viability of solar-powered aviation on a global scale.
One of the most challenging segments of the journey was the flight from Nagoya, Japan, to Hawaii. This leg lasted 118 hours and 43 minutes—nearly five days and nights—of continuous flight. During this time, pilot André Borschberg managed with minimal sleep, taking short 20-minute naps while relying on autopilot. The circumnavigation of Solar Impulse 2 highlighted the potential of clean energy in aviation. Bertrand Piccard reflected, “The goal was not to transport passengers but to transport a message: to show what we can achieve with clean technologies.”
“The goal was not to transport passengers but to transport a message: to show what we can achieve with clean technologies.”
Bertrand Piccard
How It Flies at Night
A remarkable aspect of Solar Impulse’s design is its ability to fly at night. This capability is made possible by the aircraft’s lithium-ion batteries, which store excess energy collected during the day. These batteries allow the plane to continue flying after sunset.
During daylight, Solar Impulse ascends to approximately 8,500 meters (about 28,000 feet) to maximize sunlight absorption by its solar cells. As night falls and the aircraft descends, it switches to battery power. The stored energy is used to keep the electric motors running through the night. By morning, the aircraft can climb again and recharge its batteries, maintaining a continuous cycle of day and night flying.
What Happened to Solar Impulse Eventually?
In September 2019 SI Foundation sold the SI 2 aircraft to Skydweller, a Spanish-American company. It is developing autonomous unmanned aerial vehicles capable of continuous flight. As part of this sale, they transferred SI 2 aircraft from Switzerland to Spain. However, once Skydweller completes its research and development flights they will transfer the Solar Impulse 2 back to Switzerland for permanent display at the Swiss Museum of Transport.
Adapting Solar Technology to Passenger Aircraft
Looking ahead, researchers are exploring ways to apply the technology behind Solar Impulse to larger passenger aircraft. Although Solar Impulse was not designed for commercial use, its success has inspired further developments in solar-powered aviation.
Scaling up solar-powered aircraft presents challenges, particularly in energy efficiency. While Solar Impulse could fly with the weight of a car, passenger planes require significantly more power to lift multiple passengers. Advances in solar cell efficiency and battery storage could make larger solar-powered aircraft feasible in the future.
The future of aviation might include hybrid aircraft combining solar power with other renewable energy sources, such as hydrogen fuel cells. This approach could further reduce the carbon footprint of air travel and bring the industry closer to achieving net-zero emissions.
Conclusion
Solar Impulse represents a pioneering achievement in both aviation and renewable energy. From its inception as a visionary project to its successful circumnavigation of the globe, the aircraft has showcased the potential of clean technologies in air travel. While not designed for commercial use, the innovations and insights gained from Solar Impulse are paving the way for a future of sustainable aviation. As research progresses, solar-powered planes carrying passengers may one day become a reality, contributing to a cleaner and greener planet.
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