"Big day for space station. Congratulations," Mission Control radioed space shuttle Atlantis as the electricity generating panels glinted like gold bars in the sunlight. “We're all extremely happy."
The unfurling of the 72-metre wings was delayed about three hours because of a software glitch involving the hardware's Ferris wheel-like rotating joint.
That mechanism allows the solar panels to move with the sun to maximise the amount of electricity generated.
The crew did not run into any trouble with the folded-up panels sticking together in the cold, a problem that came up during a mission in 2000.
This time, NASA devised a method for unfurling the solar wings that allowed them to be heated up by the sun.
The solar wings - part of a new, addition that arrived aboard Atlantis earlier this week - were folded up and mounted on blankets during the ride into space.
They will provide about a quarter of the space station's power when the orbiting outpost is completed in 2010.
The flight marks the first time since the Columbia disaster three-and-a-half years ago that construction on the half-built space station has resumed.
The new piece was installed during two spacewalks earlier this week.
Astronauts Joe Tanner and Heidemarie Stefanyshyn-Piper will again put on their spacesuits later tonight to conduct the third and final spacewalk of the 11-day mission.
Among other things, they will replace an antenna and gather up science experiments.
Atlantis undocks from the space station on Sunday and will return home on Wednesday.