Up, up and away
The Solar Impulse, a solar-powered plane that can fly both day and night using power stored in its lithium-ion batteries, made its maiden voyage in 2009, traveling 1,150 feet at an altitude of just over 3 feet. It has since completed much farther (and higher) flights, has flown overnight, internationally and even intercontinentally.
The plane harnesses the sun's energy using 11,628 photovoltaic cells. Its 208-foot wingspan is roughly that of a jumbo jet, but it weighs only as much as a car. It has a cruising speed of 44 mph and carries one person at a time.
The Solar Impulse recently completed a journey across the U.S. in stages, and it's set to fly around the world in 2015.