Hooray?: "Advanced" solar-powered plane can't fly in bad weather, goes 43 miles per hour, has a single-seat cockpit, weighs 3,500 pounds loaded, and has about as much power as the Wright brothers' first planes

Solar-powered plane wraps first leg of flight across United States | Reuters

The flight crew plans pauses at each stop to wait for favorable weather. It hopes to reach John F. Kennedy International Airport in New York in about two months.

Swiss pilots and co-founders of the project, Bertrand Piccard and Andre Borschberg, will take turns flying the plane, built with a single-seat cockpit.
...
The aircraft is propelled by energy collected from 12,000 solar cells built into the wings that simultaneously recharge four large batteries with a storage capacity equivalent to a Tesla electric car that allow it to fly after dark.

The lightweight design and wingspan allow the plane to conserve energy, but make it vulnerable. It cannot fly in strong wind, fog, rain or clouds.

The plane can climb to 28,000 feet and flies at an average of 43 miles per hour (69 km per hour).

The project began in 2003 with a 10-year budget of 90 million euros ($112 million) and has involved engineers from Swiss escalator maker Schindler and research aid from Belgian chemicals group Solvay.

Solar Impulse - Wikipedia, the free encyclopedia

Loaded weight: 1,600 kg (3,500 lb)

Solar Impulse departs for first sun-powered flight across US - CSMonitor.com

it's possible solar power will never be a viable option for mainstream passenger air travel.

"For a solar power airplane to be commercially viable it has to be fast," Bob van der Linden, chairman of the aeronautics division at the Smithsonian National Air and Space Museum, said in a telephone interview. "That means jet power, not solar power."

The Solar Impulse's engines put out 10 horsepower, about as much power as the Wright brothers' first planes. It can fly at only a little better than half the speed that Charles Lindbergh did when he made the first solo nonstop flight across the Atlantic Ocean in 1927.

What is the horsepower of one engine in a Boeing 747

So, the peak power output of ONE engine is approximately 30,000 hp.

Note that if this plane takes 60 days to travel between SF to NY, that really isn't very impressive when you consider what sailboats and cyclists have done:
Sailboat Crew Breaks Speed Record in NY-to-SF Voyage | Playbook | Wired.com

The crew pulled into San Francisco Bay aboard the VOR70 Maserati on Saturday, precisely 47 days and 42 minutes after leaving New York and sailing around Cape Horn, following a challenging 13,225-mile route made popular during the Gold Rush — hence the name.

Cycling record coast to coast? - Yahoo! Answers

8 days, 9 hours, 47 minutes over a 3,107 mile course.

Solar Challenger - Wikipedia, the free encyclopedia

In 1981, it successfully completed a 163 mile (262 km) demonstration flight from France to England