An airplane powered by the sun

The Solar Impulse team members were cheering on Thursday as their experimental solar-powered plane completed its first 24-hour test flight successfully, proving that the aircraft can collect enough energy from the sun during the day to stay aloft all night.

The test brings the Swiss-led project one step closer to its goal of circling the globe using only energy from the sun.

But while the team says this proves that emissions-free air travel is possible, it doesn't see solar technology replacing conventional jet propulsion any time soon.

Instead, the project's overarching purpose is to test and promote new energy-efficient technologies. (AP Photo)

Pilot Andre Borschberg eased the Solar Impulse out of the clear blue morning sky onto the runway at Payerne airfield at 9 am on Thursday morning. (AP Photo)

The plane soaked up the sunshine as Borschberg flew gentle loops over the Jura mountains west of the Swiss Alps.

This week's attempt was described as a "milestone" by the team and comes after seven years of planning. (AP Photo)

Borschberg, a 57-year-old former Swiss fighter endured freezing conditions during the night and ended the test flight with a picture-perfect landing to cheers and whoops from hundreds of supporters on the ground. (AP Photo)

Earlier this year, the plane took to the skies for its maiden flight.

During the 90-minute flight, the plane completed a series of turns by gently tilting its black-and-white wings,as wide as those of a 747 jumbo jet. It had climbed nearly a mile above the Swiss countryside then.

Here are some pictures from the plane's maiden flight.(AP Image)

The Solar Impulse lifted off from a military airport at a speed no faster than 28 mph (45 kph) after briefly accelerating down the runway.

It slowly gained altitude above the green-and-beige fields and eventually faded into the horizon as villagers watched from the nearest hills. (AFP Image)

The weather was sunny, and there was little wind — obvious advantages for a plane so light and dependent on the sun. (AP Image)

The Solar Impulse reached an altitude of 5,500 feet. (AP Image)

During Wednesday's 90-minute flight, the plane completed a series of turns by gently tilting its black-and-white wings, which are as wide as those of a 747 jumbo jet. It climbed nearly a mile above the Swiss countryside.(AP Image)

After a gentle landing, Test pilot Markus Scherdel emerged from the cockpit with his arms raised, and the team broke open bottles of champagne. (AP Image)

Co-pilot Andre Borschberg followed the flight in a helicopter. Below waited numerous people involved with the project and Piccard, who comes from a long line of adventurers. His late father, Jacques, was an oceanographer and engineer who plunged deeper beneath the ocean than any other man. His grandfather Auguste, also an engineer, was the first man to take a balloon into the stratosphere. (AP Image)

Engineers on the $93.5 million (€70 million) project have been conducting short tests since December, taking the plane no higher than 2 feet and flying no more than 1,000 feet in distance. (AP Image)

A night flight is planned before July, and then a second plane will be built based on the results of those tests.

That plane will be the one to attempt the round-the-world flight planned for 2012. (AFP Image)

Using almost 12,000 solar cells, rechargeable lithium batteries and four electric motors, Piccard and co-pilot Andre Borschberg plan to take the plane around the world. They will make regular stops to switch places and stretch after long periods in the cramped cockpit — and to show off their aircraft.(AP Image)

When the plane attempts to circle the globe, the team will have to monitor conditions closely to ensure the aircraft follows the best weather. Ground crews will stay close to provide service at each stop, Scherdel said. (AP Image)

Elaborating on the problems and dilemmas they had to encounter during the project, Project leader Bertrand Piccard said that there has never been an airplane of that kind - so big, so light, using so little energy that could fly! So there were huge question marks for them. (AP Image)

"The first crucial question was: Do we have enough power to fly?" said Borschberg. "The second crucial thing was: Are we capable of landing this airplane, is it controllable?"

"It was two hours of deep emotion," he added, calling the test flight the high point of seven years of work on the project. "The airplane has landed but we have not yet landed." (AP Image)

Test pilot Markus Scherdel said Wednesday's flight proved that the plane could take off and land safely and handles like a passenger jet.

Aviation experts said they see a future for renewable fuels in commercial aviation, but they predicted that biofuels from plants, algae or other sources were more likely to succeed than solar power. (AP Image)