All-Solar Plane Completes Historic Pacific Crossing by David Z. Morris @FortuneMagazine April 24, 2016, 12:37 PM EDT E-mail Tweet Facebook Linkedin Share icons Solar Impulse 2, a long-distance plane powered entirely by solar energy, touched down late last night at Moffett Airfield in Mountain View, California, after a 62 hour flight from Hawaii. The flight came after a nine-month pause in the plane’s planned circumnavigation of the Earth, a project intended to highlight environmental issues and clean technology. The trip is now a little over halfway complete. Get Data Sheet, Fortune’s technology newsletter. Solar Impulse 2 is a daring effort both technologically and, for the two men sharing pilot duties, personally. Solar cells along the plane’s huge wingspan charge its batteries during the day, allowing it to keep flying at night. But its huge wings and light weight also make the plane very vulnerable to weather. It’s guided by a solo pilot, who occupies a tiny cabin—and actually sleeps for short stretches while the plane flies on autopilot. The Hawaii to California flight was piloted by Bertrand Piccard, a psychiatrist and explorer, who alternates duties with engineer André Borschberg. The two also co-head the overall project. The plane’s arrival in California represents a major recovery after problems with the plane’s batteries during the July 2015 flight from Japan to Hawaii. That five-day journey shattered the record for the longest solo flight of any kind, but the unexpected demands of takeoff in a tropical climate damaged the plane’s batteries, necessitating the nine-month layover in Hawaii for repairs. For more on solar tech, watch our video. From Mountain View, Solar Impulse 2 will head towards New York City, with a stopover in the Midwest. The final leg of the trip will entail stops in Southern Europe or Northern Africa, and finally, a return to Abu Dhabi, where the plane first lifted off in March of 2015.