In pics | Back to Abu Dhabi, Solar Impulse 2 completes round-the-world trip

On Tuesday, Solar Impulse 2 landed in the UAE, completing its epic journey to become the first sun-powered airplane to circle the globe without a drop of fuel to promote renewable energy.

The plane touched down at 04.05am in the capital Abu Dhabi after a more than 48 hour-long flight from Cairo, the final leg in its circumnavigation which began on March 9 last year.

Cheers and clapping welcomed the plane as it arrived at Al-Bateen Executive Airport, where it first launched its world tour, an AFP journalist reported.

Swiss explorer and project director Bertrand Piccard was in the cockpit during the 2,763 km flight from Cairo, crossing the Red Sea, the vast Saudi desert and flying over the Gulf.

The flight capped a remarkable 42,000km journey across four continents, two oceans and three seas.

It took off from Cairo on the final leg early on Sunday, having previously crossed Asia, North America, Europe and North Africa.

“The future is clean, the future is you, the future is now, let’s take it further,” said Piccard as he disembarked.

Hours before landing, UN secretary general Ban Ki-moon expressed praise in a live-streamed conversation with Piccard.

“My deepest admiration and respect for your courage,” he said.

“This is a historic day, not only for you but for humanity.”

‘Achieve the impossible’

Dubbed the “paper plane”, Solar Impulse 2 has been circumnavigating the globe in stages, with 58-year-old Piccard and his compatriot Andre Borschberg taking turns at the controls of the single-seat aircraft.

Borschberg, 63, smashed the record for the longest uninterrupted journey in aviation history with the 8,924-kilometre flight between Nagoya, Japan and Hawaii that lasted nearly 118 hours.

“The adventure began 13 years ago... #futureisclean,” he tweeted on Monday.

No heavier than a car but with the wingspan of a Boeing 747, the four-engine battery-powered aircraft relies on around 17,000 solar cells embedded in its wings.

The plane has clocked an average speed of 80kph.

The pilots use oxygen tanks to breathe at high altitude and wear suits specially designed to cope with the extreme conditions.

They have had to withstand temperatures inside the tiny cockpit ranging from minus 20°C to plus 35°C (minus 4°to plus 95°F).

Piccard has said he launched the project in 2003 to show that renewable energy “can achieve the impossible”.

His dream has taken much longer than planned. The attempt was initially expected to last five months, including 25 days of actual flying.

But the aircraft was grounded in July last year when its solar-powered batteries suffered problems halfway through the trip.

‘For a better world’

The project has also been beset by bad weather and illness, which forced Piccard to delay the final leg.

While in the air, the pilot is constantly in contact with mission control in Monaco, where a team of weathermen, mathematicians and engineers monitors the route and prepares flight strategies.

“It’s a project for energy, for a better world,” Piccard told journalists in Cairo before taking off.

A psychiatrist who made the first non-stop balloon flight around the world in 1999, Piccard had warned the last leg would be difficult because of the high temperatures.

“It’s been two hours now I’m flying into high up and down drafts. And I can’t even drink. It’s really exhausting,” he tweeted on Sunday.

Speaking to the BBC from the cockpit, Piccard described the final stage as a “fantastic moment” and likened the plane to a “flying laboratory”.

“We are testing all these new, clean and modern technologies in order to fly with an endless endurance,” he said.

While the pilots do not expect commercial solar-powered planes any time soon, they hope the project will help spur wider progress in clean energy.

“We have new insulation material, new LED lamps, we have new extremely light carbon fibre structures... All this can be used now on the ground,” Piccard said.

“It’s a complete revolution in the protection of the environment.”