An aircraft powered by solar energy left Egypt on Sunday on the last leg of the first ever fuel-free flight around the globe. Solar Impulse 2, a spindly single-seat plane, took off from Cairo in darkness en route to Abu Dhabi, its final destination, with a flight expected to take up to 72 hours, Reuters reported. The plane, which began its journey in Abu Dhabi in March 2015, has been piloted in turns by Swiss aviators Andre Borschberg and Bertrand Piccard in a campaign to build support for clean energy technologies. "The world flight ends in Abu Dhabi, but not the project," Piccard told Reuters a few days before takeoff. Solar Impulse flies without a drop of fuel, its four engines powered solely by energy collected from more than 17,000 solar cells in its wings. It relies on solar energy collected during the day and stored in batteries for electrical energy to fly at night.
