The Solar Impulse glides over the Golden Gate Bridge in San Francisco during a test flight last week. The plane, which is powered by about 12,000 photovoltaic cells, is scheduled to begin a cross-country tour within the next week. (Solar Impulse via Associated Press)

A solar-powered plane that can fly at night is gearing up to be the first airplane of its kind to fly across the United States.

The Solar Impulse has spent the past few weeks around San Francisco, California, taking practice runs before its cross-country tour.

“That’s a mythical step in aviation,” Andre Borschberg, one of the plane’s pilots and creators, said about flying cross-country. He compared the Solar Impulse team to early-20th-century aviators who tried to fly coast to coast in propeller planes.

He said a solar-powered trip around the world could happen in two years.

The Solar Impulse is powered by about 12,000 photovoltaic cells. They cover the plane’s massive wings and charge its batteries, allowing it to fly day and night without fuel. It has the wingspan of a large passenger airplane but the weight of the average family car, a combination that makes it vulnerable to bad weather.

Its creators say the Solar Impulse is designed to showcase the potential of solar power and will never replace fuel-powered commercial flights. The delicate, single-seat plane cruises at around 40 miles per hour —a lot slower than ordinary planes — and it can’t fly through clouds.

Borschberg and Bertrand Piccard, Solar Impulse’s co-founder and chairman, had predicted that the plane would be ready for the cross-country journey this week, depending on the weather. “We like nice weather,” Borschberg said. “We like sunny days,”

Friday is now the first possible day for takeoff, a Solar Impulse spokeswoman said Monday.

Stops are planned in Phoenix, Arizona; Dallas, Texas; Northern Virginia; and New York, with conferences and events in each city. Each flight leg will take 20 to 25 hours, with 10-day stops in each city. The plane is expected to be at Dulles International Airport from late June until mid-July.

Between Dallas and Dulles, the plane will stop at one of three other cities: Atlanta, Georgia; Nashville, Tennessee; or St. Louis, Missouri.

Borschberg said his group is close to being able to launch the nonstop flights needed to go around the world. Using solar power, “we are close to the notion of perpetual flight,” he said.

— Associated Press