Solar Impulse 2, a solar-powered aircraft landed in Abu Dhabi on Tuesday, completing the first fuel-free flight around the world. It took 16 months due largely to problems along the way. The two pilots, Swiss explorers Bertrand Piccard and André Borschberg, flew the 500 hours required.
The propeller-driven aircraft’s four engines are powered exclusively by energy collected from more than 17,000 solar cells built the plane’s wings. Excess energy is stored in four batteries during daylight hours to keep the plane flying after dark.