The single-seat plane took off from Cairo at 1:30 a.m. local time Sunday, en route to Abu Dhabi, its starting point in March 2015 and its final destination. The flight is expected to take between 48 and 72 hours.

Solar Impulse 2 arrived in Cairo after a two-day flight from Spain, finishing the 3,745-kilometer (2,327-mile) journey with an average speed of 76.7 kilometers per hour (47.7 miles per hour). On June 23, it became the first solar-powered aircraft to cross the Atlantic Ocean, flying 70 hours from New York to Seville, Spain.

Borschberg flew the plane over the pyramids of Giza on July 13

The plane has been piloted in turns by Swiss aviators Andre Borschberg and Bertrand Piccard. The project is designed to build support for clean energy technologies.

"The round-the-world flight ends in Abu Dhabi, but not the project," Piccard told news agency Reuters some time before takeoff. "The project is a big promotion of clean technologies around the world and the legacy of Solar Impulse is the created international community," he said.

"I started to dream about this project 17 years ago in 1999 when I finished my hot-air balloon landing in Egypt, so 17 years later I take off where the balloon landed," Piccard went on.

The plane's four engines are powered solely by energy collected from over 17,000 solar cells in its wings, relying on solar energy collected during the day and stored in batteries for electrical energy to fly at night.

The carbon fiber plane can climb to 8,500 meters (28,000 feet) and cruise at 55-100 kilometers per hour.

Watch video 00:39 Solar Impulse 2 completes first-ever Atlantic flight

jbh/cmk (dpa, Reuters, AFP)