Solar Impulse flying over the Statue of Liberty in New York last month

Solar Impulse 2 completes record-breaking round-the-world flight

Solar Impulse 2, a plane powered only by energy from the Sun, has completed its 15-month mission to circumnavigate the world.

Landing in Abu Dhabi yesterday - where it first took off in March 2015 - the plane finally completed its epic 25,000-mile record-breaking journey.

The feat is the world's first round-the-world flight to be powered solely by the sun.

The Swiss-engineered plane has made 16 stops across the world during the journey without using any fuel, in an attempt to prove the viability of renewables, encourage lower energy consumption and save natural resources.

"Our mission now is to continue to motivate people, corporations and governments to use these same solutions on the ground wherever they make sense," Solar Impulse chairman and pilot Bertrand Piccard said in a statement.

The aircraft is powered by 17,248 solar cells that transfer energy to four electrical motors that power the plane's propellers.

It runs on four lithium polymer batteries at night and has a wingspan that stretches to 71 metres - the same as a Boeing 747 - to catch the sun's energy.

Unlike that passenger jet, Solar Impulse weighs only 2300kgs - about as much as a mini-van or mid-sized lorry - and was steadied by runners and cyclists during take-offs and landings. An empty Boeing 747, by comparison, weighs approximately 181,000kgs.

Despite the achievement of its historic mission, Solar Impluse 2's journey was far from quick or problem-free.

The pilots faced a nine-month delay during 2015 after the plane's batteries were damaged during a flight from Japan to Hawaii. 

It was also delayed for over a week in Cairo, ahead of its final flight to Abu Dhabi, when Piccard fell ill and due to poor weather conditions.

During its entire mission, Solar Impluse 2 completed more than 500 flight hours, cruising at an average speed of between 28 and 56mph.

It made stops in Oman, India, Burma, China, Japan, the US, Spain, Italy, Egypt and the United Arab Emirates. Its North American stops included California, Arizona, Oklahoma, Ohio, Pennsylvania and New York.

The carbon-fibre plane is a single-seater aircraft, meaning its two Swiss pilots - Piccard and Andre Borschberg - took turns flying solo for long days and nights.

To calm their minds and manage fatigue during the long solo flights, Borschberg practised yoga and Piccard self-hypnosis.

"By flying around the world thanks to renewable energy and clean technologies, we have demonstrated that we can now make our world more energy efficient," Borschberg said.

The pilots would rest a maximum of 20 minutes at a time, repeating the naps 12 times over each 24-hour stretch.

While neither pilot was able to stand in the cockpit while flying, the seat reclined for stretching and its cushion could be removed for access to a toilet.

Goggles worn over the pilot's eyes flashed lights to wake him up while armbands worn underneath their suits buzzed when the plane was not at flying level.

The plane also lacked a pressurized cockpit, so the pilots could feel changes in temperature and their blood oxygen levels were monitored and sent back to ground control in Monaco.

Piccard previously became the first person to circumnavigate the globe non-stop in a hot air balloon in 1999, while Borschberg is an engineer and graduate of the Massachusetts Institute of Technology. The Solar Impulse project was launched by the pair in 2003.

At an estimated cost of more than £76m, the pair received substantial funding from its primary sponsor, UAE-based Masdar, which is Abu Dhabi government's clean-energy company.

40 additional sponsors, including Omega, Belgian chemical company Solvay, Swedish-Swiss automation corporation ABB, Swiss manufacturer Schindler, Google and Moet Hennessey also helped fund the project.

"More than an achievement in the history of aviation, Solar Impulse has made history in energy," Piccard told a large crowd on landing.

"I'm sure that within the next 10 years we'll see electric airplanes carrying 50 passengers on short to medium-haul flights," he said, before noting that the technologies used on Solar Impulse 2 could be used on the ground in daily life to halve carbon dioxide emissions.

Solar Impulse 2 infographic

Solar Impulse 2 infographic  

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