The plane had been due to leave early Sunday but this was put off, apparently because of concerns over the weather.
Takeoff for Seville in Spain is now scheduled for 2:00 am (0600 GMT), the Solar Impulse team said on Twitter.
The flight over the ocean is scheduled to last 90 hours, during which solo pilot Bertrand Piccard will only be able to take short naps.
This will be ‘the longest distance we have had to fly this year,’ the team said.
The plane, no heavier than a car but with the wingspan of a Boeing 747, is being flown on its 35,000 kilometer (22,000-mile) round-the-world journey by two pilots taking turns, Swiss entrepreneur Andre Borschberg and Piccard, a psychiatrist.
The slow-moving aircraft landed at New York's John F. Kennedy International Airport on June 11, one minute ahead of schedule after a five-hour flight from Lehigh Valley in Pennsylvania.
That was the 14th leg of a journey that began March 9, 2015 in Abu Dhabi, and has taken the aircraft across Asia and the Pacific to the United States with the sun as the plane's only source of power.
The single-seat aircraft is clad in 17,000 solar cells. During night-time flight it runs on battery-stored power.
It features four propellers and has an average air speed of 75 kilometers per hour (47 mph).
