Solar Impulse 2's Hawaii leg started early Monday, after a month-long, unscheduled stop over at Japan.

The solar-powered plane has been on a mission to circumnavigate the globe with no fuel, and this is its last flight back to U.S. soil.

It departed 3 a.m. from Nagoya airport in central Japan with pilot André Borschberg. It is on its journey to break the record for longest flight, with the journey set to last for five days and five nights - about 120 hours.

Due to the unique features of the plane, it needs the right weather conditions before being allowed to take-off. Officials only made announcements of the departure when they were sure that the flight could actually continue.

"A formal communiqué will be issued once Solar Impulse has passed the Point of No Return and that we know that the pilot is on a safe track to reach Hawaii," the press team said in an email to journalists, Fox News reports.

The plane is equipped with 17,000 solar cells, located on its wings. The cells recharge the batteries that enable it to fly. Daytime flight level is at 8,534 meters while at night, the plane only flies at 2,438 meters.

The sun is expected to rise and start powering the plane again around 4:30 p.m. EDT., CBC News reports.