The four-engine Solar Impulse, whose wingspan greatly exceeds its fuselage length for maximum lift, took off from Switzerland's Payerne airbase early Wednesday and returned at dawn Thursday. Pilot Andre Borschberg flew the craft to an altitude of 8,654 meters while achieving a top ground speed of 68 knots.
"It was unbelievable, success better than we expected," Borschberg, a Swiss air force veteran, told Reuters television. "We almost thought to make it longer, but we demonstrated what we wanted to demonstrate so they made me come back," he said.
Solar Impulse features 12,000 solar panel designed to capture solar energy. Its gangly, 63.4 meter wingspan and relatively light 3,500 lb airframe help it to soar with minimal power requirements.
Organizers said the project shows the potential of solar energy and other reusable sources of power. "This is a highly symbolic moment," said Bertrand Piccard, initiator and president of Solar Impulse, in a statement. "Flying by night using solely solar power is a stunning manifestation of the potential that clean technologies offer today to reduce the dependency of our society on fossil fuels," Piccard said.
The project plans to begin construction of a second solar-powered aircraft, which will be tasked with flying across the Atlantic using only the sun's energy.
A group of commercial sponsors, including Belgian chemicals producer Solvay, watchmaker Omega, and Deutsche Bank have put up about $95 million to help fund the effort.