The plane, which runs on four electric propellers powered by 12,000 solar cells mounted on the plane's 63-meter wingspan, touched down in the dark at Dulles International Airport at 12.15 am (1415 GMT).
The Solar Impulse usually lands in the middle of the night, when traffic at the airports has subsided.
At the controls was Swiss pilot Bertrand Piccard, who is taking turns with compatriot Andre Borschberg on different legs of the flight across the United States.
The Solar Impulse landing was broadcast live on the organizer's website, live.solarimpulse.com.
The aircraft can fly at night by reaching a high elevation of 27,000 feet (8,230 meters) and then gently gliding downward, using almost no power until the sun comes up to begin recharging the solar cells.
The flight from Cincinatti, Ohio took about 14 hours, after a 14-hour pit stop in the midwestern US city prompted by difficult weather.
The organizers had planned for the solar craft to fly directly from St. Louis, Missouri to Washington DC, but strong cross and head winds slowed down the aircraft, organizers said in a statement.
The conditions were such that the flight to Washington would have taken longer than the self-imposed 24-hour time limit set for the pilot in the cramped single-seater cockpit.
The Solar Impulse project, founded and led by Piccard and Borschberg, aims to showcase what can be accomplished without fossil fuels, and has set as its "ultimate goal" a round-the-world flight in 2015.
The first leg of Solar Impulse's US tour took place on May 3, when Piccard flew the aircraft from the San Francisco, California, to Phoenix, Arizona.
St. Louis was chosen as the Midwest stopover as a homage to aviation pioneer Charles Lindbergh and his "Spirit of St. Louis," the first plane to fly from New York to Paris non-stop.
source: interaksyon.com
