Solar Impulse completes historic round-the-world flight

An aircraft powered by solar energylanded in Abu Dhabi, United Arab Emirates early Tuesday, after flying 40,000 kilometres around the world without the use offossil fuels.

The Solar Impulse team held a post-landing news conference following the historic flight, which featured a video compilation from the year-long journey.

Since its March 2015 take off, the Swiss-engineered Solar Impulse 2 has made 16 stops across the world without using a drop of fuel to demonstrate that using the plane's clean technologies on the ground can halve the world's energy consumption, save natural resources and improve quality of life.

After landing the plane, pilotBertrandPiccardwas greeted outside the cockpit by his Solar Impulse partner and fellow pilot AndreBorschberg. They hugged and pumped their fists in the air.

"The future is clean. The future is you. The future is now. Let's take it further,"Piccardsaid, speaking through a microphone to applause and cheers from a crowd that included Prince Albert of Monaco.

At the press conference, Borschberg said Piccard was chosen for the final leg of the journey because it was his vision all along, "today, the vision is reality."

Piccard said when he touched the wheels down in Abu Dhabi, he thought "this is a start. There is no excuse not to continue."

Powered by solar cells

The aircraft is uniquely 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. The plane's wingspan stretches 72 metres to catch the sun's energy.

At around 2,300 kilograms, the plane weighs about as much as aminivanor mid-sized truck. An empty Boeing 747, in comparison, weighs 180,000 kilograms. To help steady it during takeoffs and landings, the plane was guided by runners and bicyclists.

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

The pilots faced a nine-month delay a year ago after the plane's batteries were damaged during a flight from Japan to Hawaii. It was also delayed for more than a week in Cairo ahead of its final flight to Abu Dhabi whenPiccardfell ill, and due to poor weather conditions.

Over its entire mission, Solar Impluse 2 completed more than 500 flight hours, cruising at an average speed of between 45 km/h and 90 km/h. It made stops in Oman, India, Myanmar, China, Japan, the U.S., 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 Piccardand Borschberg had to take turns flying solo for long days and nights. To calm their minds and manage fatigue during the long solo flights,Borschbergpracticed yoga andPiccardself-hypnosis.

In a statement this week,Borschbergsaid it is no longer a question of whether it's possible to fly without fuel or polluting emissions.

"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," he said.

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

It took 70 hours forPiccardto cross the Atlantic Ocean, which was the first by a solar-powered airplane.

Borschberg's flight over the Pacific Ocean at 118 hours or what is five days and five nights shattered the record for the longest flight duration by an aircraft flying solo.

Neither pilot was able to stand in the cockpit while flying, but 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 placed underneath their suits buzzed when the plane was not at flying level.

Pilots in non-pressurized environment

The plane also did not have a pressurized cockpit soBorschbergandPiccardcould feel changes in temperature. The pilot's blood oxygen levels were monitored and sent back to ground control in Monaco.

Hot temperatures in the Middle East this time of year cause thermals and turbulence that forcedPiccardto fly longer periods of time with an oxygen mask as he piloted the last leg of the trip from Cairo to Abu Dhabi in roughly three nights and two days.

Piccard, a psychiatrist, is the son of undersea explorer JacquesPiccardand a grandson of balloonist AugustePiccard. In 1999, he became the first person to circumnavigate the globe non-stop in a hot air balloon.

Borschberg, an engineer and graduate of Massachusetts Institute of Technology, is also an entrepreneur. He launched the Solar Impulse project in 2003 withPiccard.

The project is estimated to cost more than $100 million. The UAE-based Masdar, the Abu Dhabi government's clean-energy company, was a main sponsor of the flight. There were more than 40 additional sponsors, including Omega, Belgian chemical company Solvay, Swedish-Swiss automation corporation ABB, Swiss manufacturer Schindler, Google and Moet Hennessey, among others.