Solar Impulse 2 (Si2) is a solar-powered plane that is capable of flying both in daytime and at night. Its inaugural flight was made in June last year, when it took to the skies for just over two hours, but the latest iteration will be able to comfortably cross oceans and continents –flying without fuel for five consecutive days and nights at a time.
The Solar Impulse project began in 2003, but a 70-person team had to work for six years before the first working prototype was able to make its debut in 2009.
The second prototype of the sun-powered vehicle has a 72-metre wingspan, slightly larger than that of a Boeing 747, but weighs just 2,300 kilograms, approximately the same as a family car.
Completed in April 2014, Solar Impulse 2 has 17,248 solar cells built into its wings, which supply four electric motors with enough energy for the machine to fly. During the day these cells recharge lithium batteries, allowing Solar Impulse 2 to operate during nighttime as well.
A 3.8-metre cockpit sits at the front of the plane, and has been specially designed so that the pilot can live within the space for up to one week. Unlike most aircraft, the cockpit is not pressurised in order to keep the overall weight of the vehicle to a minimum.
The plane's 21,700-mile expedition will begin in Abu Dhabi, where the emirate-backed renewable energy company Masdar first displayed the vehicle for Abu Dhabi Sustainability Week last year.
Once the plane sets off, 12 stops are planned for its globe-spanning flight: southern Europe or northern Africa; New York City; the American Midwest; Phoenix, USA; Hawaii, USA; Nanjing, China; Chongqing, China; Mandalay, Myanmar; Ahmedabad, India; Varanasi, India; and Muscat, Oman.
It is expected the trip will take five months in total, with stop-offs at each location for the Solar Impulse team and pilots to engage in discussions about renewable energy. Corporate partners for the flight include Google, Bayer, and Swisscom.
"We want to demonstrate that clean technology and renewable energy can achieve the impossible," said Solar Impulse chairman Bertrand Piccard in a statement.
"We want youth, leaders, organisations and policymakers to understand that what Solar Impulse can achieve in the air, everyone can accomplish on the ground in their everyday lives."
Co-founder André Borschberg pointed out that Solar Impulse is not the first aircraft to function on solar power alone, but that it is the first capable of crossing oceans and continents.
"Now we have to ensure the sustainability of the pilot in order to complete the route," he said. "Solar Impulse 2 must accomplish what no other plane in the history of aviation has achieved – flying without fuel for five consecutive days and nights with only one pilot in the unpressurised cockpit."
The public can follow the journey at Solar Impulse's official website.