The Solar Impulse 2, an experimental aircraft flying around the world to draw attention to clean energy technologies, took off Monday from near San Francisco en route to the southwest city of Phoenix.

Pilot Andre Borschberg took to the air just after 5:00 am (12:00 GMT). The plane had been in California for a week since crossing the Pacific to land in Mountain View.

Borschberg, who has been alternating the long solo flights with his teammate, Swiss adventurer Bertrand Piccard, will pilot Solar Impulse across the United States and to New York. Piccard piloted the craft from Hawaii to California.

‘The sun is rising in the horizon. It feels good to be flying round-the-world with #Si2 again,’ Borschberg posted on Twitter.

The 63-year-old adventurer took off at the early hour to take advantage of a clear weather window as he flies to Phoenix Goodyear Airport in Arizona, which should take about 16 hours and 20 minutes. The plane is crossing some 720 miles (1,160 kilometers) over the Mojave Desert.

The takeoff from Moffett Airfield southeast of San Francisco marked the beginning of the 10th of 13 legs in a journey that began last year in the United Arab Emirates.

The mission aims to promote the use of renewable energy, with an aircraft powered by 17,000 solar cells.

The plane's wingspan is wider than that of a jumbo jet but its weight is roughly the same as a family car.

Solar Impulse 2 was grounded in July last year when its batteries suffered problems halfway through its 21,700-mile (35,000-kilometer) circumnavigation.

The crew took several months to repair damage from tropical high temperatures during the first Pacific stage, a 4,000-mile flight between Japan and Hawaii.

The aircraft was flown on that leg by Borschberg, whose 118-hour journey smashed the previous record of 76 hours and 45 minutes set by US adventurer Steve Fossett in 2006.

Born in Zurich, Borschberg is no stranger to adventure -- 15 years ago he narrowly escaped an avalanche, and then in 2013 he was involved in a helicopter crash that left him with minor injuries.

He took catnaps of only 20 minutes at a time to maintain control of the pioneering plane during his arduous flight from Japan, in what his team described as ‘difficult’ conditions.

Piccard, a 58-year-old doctor by training, already completed the first non-stop round-the-world balloon flight in 1999.

The solar-powered plane, which stores energy in batteries for when the sun is not shining, will stop in New York before a transatlantic flight to Europe. From there, the pilots plan to make their way back to the point of departure in Abu Dhabi.