Solar-powered plane's remarkable flight around the world

Over its entire mission, Solar Impulse 2 cruised at altitudes of up to 9,000 metres and at an average speed of between 45 and 90 km per hour.

A solar-powered aircraft successfully completed the first fuel-free flight around the world on Tuesday, returning to Abu Dhabi after an epic 16-month voyage and demonstrating the potential of renewable energy.

The plane, Solar Impulse 2, touched down in the United Arab Emirates capital at 0005 GMT (0405 local time) on Tuesday.

IMAGE: Solar Impulse 2, the solar powered plane, piloted by Swiss pioneer Andre Borschberg is seen during the flyover of the pyramids of Giza on July 13, 2016 prior to the landing in Cairo, Egypt. Photograph: Reuters

It first took off from Abu Dhabi on March 9, 2015, beginning a landmark journey of about 40,000 km (24,500 miles) around the globe and nearly 500 hours of flying.

IMAGE: Solar Impulse 2, a solar-powered plane piloted by Bertrand Piccard of Switzerland, flies over the Golden Gate bridge in San Francisco, California.
Photograph: Jean Revillard/Reuters

Unfavourable weather at times hindered smooth flying, causing the plane to be grounded for months in some countries.

IMAGE: German test pilot Markus Scherdel steers the solar-powered Solar Impulse 2 aircraft over the Lake Neuchatel during a training flight at its base in Payerne, Switzerland. Photograph: Denis Balibouse/Reuters

Swiss explorers Bertrand Piccard and André Borschberg, Solar Impulse founders and pilots, took turns piloting the aircraft with a wingspan larger than a Boeing 747 and weighing only as much as a family car.

IMAGE: Swiss explorers Bertrand Piccard and André Borschberg, Solar Impulse founders and pilots, took turns piloting the aircraft. Photograph: Reuters

The Swiss team is campaigning to bolster support for clean energy.

IMAGE: A bird flies along with the Solar Impulse as it approaches the runway for a landing following a test flight at Moffett Field in Mountain View, California.
Photograph: Robert Galbraith/Reuters

The propeller-driven aircraft's four engines are powered exclusively by energy collected from more than 17,000 solar cells built the plane's wings.

IMAGE: Excess energy is stored in four batteries during daylight hours.
Photograph: Reuters

Excess energy is stored in four batteries during daylight hours to keep the plane flying after dark.

Over its entire mission, Solar Impulse 2 cruised at altitudes of up to 9,000 metres and at an average speed of between 45 and 90 km (12.5 and 25 miles) per hour.

IMAGE: German test pilot Markus Scherdel steers the solar-powered Solar Impulse 2 aircraft with the Mont-Blanc in background during a training flight at its base in Payerne. Photograph: Denis Balibouse/Reuters

The plane had 16 stopovers along the way including in Oman, India, Myanmar, China, Japan, the United States, Spain and Egypt.

Abu Dhabi's green energy firm Masdar is the official host partner of Solar Impulse 2.

Oil-rich Abu Dhabi is investing billions in industry, tourism and renewables to diversify its economy away from oil.