A Swiss pilot this weekend completed the first portion of a five-leg trip across the U.S. in an airplane powered by solar energy. The so-called Solar Impulse aircraft, which runs on energy collected from 12,000 solar cells
in its long wings, flew from San Francisco to Phoenix in 18 hours and 18 minutes. The solar cells simultaneously power four batteries with the storage capacity of an electric car, which allows the plane to fly in darkness. The airplane, with a 208-foot wingspan, is made of lightweight, carbon fiber materials that help it conserve energy, but its spindly structure also makes the plane unable to fly in windy or stormy conditions. Project organizers hope the five-leg journey — which will include stops in Dallas, St. Louis, and Washington and end in New York — will demonstrate the feasibility of long-distance air travel without fuel. By 2015, the project’s co-founders, Bertrand Piccard and Andre Borschberg, hope to complete a flight around the world.