Solar Impulse 2 took off from the city of Mountain View, near San Francisco, just after 5 a.m. local time (1200 UTC) on Monday.

The aircraft, which is attempting the first circumnavigation of the globe by a piloted, fixed wing plane using only energy from the sun, had spent a week in the Silicon Valley city after Borschberg's co-pilot, Bertrand Piccard, also of Switzerland, landed there following a three-day flight from Hawaii.

Before that, the onward flight had been delayed for nine months while repairs were carried out on the plane's battery system, which had suffered heat damage on its trip from Japan.

The aircraft began its voyage, aimed at drawing attention to clean energy technologies, in March 2015 in Abu Dhabi, the capital of the United Arab Emirates. It has also made stops in Oman, Myanmar, China and Japan.

After it reaches its planned next destination of Phoenix, Arizona, which will involve a 1158-kilometer (720-mile) flight over the Mojave Desert, the plane will make just two more stops in the United States before crossing the Atlantic.

Solar Impulse 2 has a cruise speed of 70 kilometres per hour (43 mph), and a take-off speed of just 35 kilometers per hour. Its wings are equipped with 17,000 solar cells to power the propellers and charge the batteries.

tj/jm (AFP, AP)