The Solar Impulse left Moffett Field in Mountain View just after dawn on Friday.
It plans to stop at Sky Harbor airport in Phoenix, Dallas-Fort Worth airport in Texas, Lambert-St. Louis airport, Dulles airport in the Washington area and New York's John F. Kennedy airport. Each flight leg will take 20 to 25 hours, with 10-day stops in each city.
The plane is powered by about 12,000 photovoltaic cells that cover massive wings and charge its batteries, allowing it to fly day and night without jet fuel.
Its creators say solar planes will never replace fuel-powered commercial flights. The goal is to showcase the potential of solar power.