Solar-powered plane soars over Golden Gate Bridge (VIDEO)

After an unexpected nine-month delay, the Solar Impulse 2 aircraft has finally completed the ninth leg of its world tour.

The fuel-free plane touched down at Moffett Airfield, California, just before midnight local time following a two-and-half day journey across the Pacific Ocean.

Piloted alternately by Swiss adventurers Bertrand Piccard and André Borschberg, the giant dragonfly-shaped aircraft has been on a mission to fly around the world without a single drop of fuel since 2015.

More than 17,000 solar cells collect energy from the sun during the day, giving the plane enough solar energy to stay powered through the night.

The solar-powered project – with a wingspan greater than a passenger jet – has accumulated more than 20,000km on this trip. With a top speed of 80km/h, the single seater flies at a snail’s pace in comparison to commercial airliners.

But the Solar Pulse 2 team say journey is focused squarely on clean technology, showing that solar power can “improve our quality of life.”

Hawaiian stopover

So far the aircraft has completed trips to 10 cities across the globe, including a detour to the Japanese shipping hub of Nagoya due to bad weather.

In July 2015, the team completed a record-breaking flight from Japan to Hawaii. The record saw Andre Borschberg pilot the plane solo for more than 117 hours.

“I feel exhilarated by this extraordinary journey. I have climbed the equivalent altitude of Mount Everest five times without much rest,” Borschberg said at the time.

The 8,924-km flight came at some cost, however. The crew later found out that the aircraft’s batteries had overheated and needed to be replaced.

The plane would stay grounded on the island of Oahu for more than nine months, until the ninth leg of its journey began last Friday.

Piccard guided the plane over the San Francisco Bay area for two hours before his triumphant landing, posing for some incredible snapshots.

The next stop for the green energy aircraft has yet to be determined, although its flight plan suggests a 30-hour flight to a city somewhere in the heart of the US.