The plane was cruising over the cold northern Pacific about 20,000ft with a nearly-full battery as night descended, according to the website that is documenting the journey of Solar Impulse 2.
After some uncertainty about winds, the plane took off from Hawaii on Thursday and was on course to land in Mountain View, California, in about three days. The crew that helped it take off was clearing out of its Hawaiian hangar and headed for the mainland for the weekend arrival.
Pilot Bertrand Piccard is flying this leg of the journey.
“We have passed the point of no return,” the team wrote on the website. “From this point onwards, Bertrand Piccard will only be moving forward with Si2.”
At one point the plane was passed by a Hawaiian Air jet whose passengers caught a glimpse of the Solar Impulse 2 before the powerful airliner left the slow-moving aircraft behind.
The aircraft landed in Hawaii in July and was forced to stay in the islands after the plane’s battery system sustained heat damage on its trip from Japan.
The aircraft started its journey in March 2015 from Abu Dhabi, the capital of the United Arab Emirates, and made stops in Oman, Myanmar, China and Japan. It’s on the ninth leg of its circumnavigation.
Mr Piccard, who is flying the latest leg of the trip, said the idea of crossing the ocean in a solar-powered plane a few years ago stressed him out, but on Thursday he was confident things would go according to plan.
Mr Piccard also said the destination in the heart of Silicon Valley is fitting. He said on his way to the airfield that the plane will land “in the middle of the pioneering spirit”.
Co-pilot Andre Borschberg, who flew the leg from Japan to Hawaii, told Mr Piccard he greatly admires his dedication and strength.
He said that the solar plane “represents what we could do on the ground in our communities”.