The tube contains 150 solar cells, wrapped around the inside of the glass. Designed and built by Fremont startup Solyndra, the tube can absorb light from any direction and convert it to electricity. Placed in a rooftop rack, the tube can even collect light bouncing off the roof.

Solyndra exits stealth mode Tuesday with $600 million in venture capital, $1.2 billion in customer contracts and a radically different approach to solar.

Solyndra's tubes, made at the company's Fremont factory, don't need to be tilted to face the sun the way traditional solar cells do. They work just as well lying flat, making them ideal for the wide-open roofs of office buildings, warehouses and big-box retail stores.

And because Solyndra's racks leave an inch of space between each tube, they don't catch the wind very easily and don't need to be bolted to the roof, cutting installation time and cost.

Solyndra Chief Executive Officer Chris Gronet said he got the idea after noticing just how much room traditional solar panels squander. Rows of standard solar panels perched on a flat roof have to sit several feet apart so they don't cast shadows on each other. Lay solar cylinders flat, however, and you can blanket the entire roof.

"Look at the picture long enough, and you're going to realize there's a lot of wasted space, and a cylinder might work better," said Gronet.

According to the company, there are some 30 billion square feet of flat roof space in the United States, just waiting to be covered. With that much space, Solyndra's tubes could generate enough power for more than 16 million homes.

University and government researchers have tinkered with solar cylinders before, said Daniel Kammen, a professor in the Energy and Resources Group at UC Berkeley. But they didn't get as far as Solyndra, which generated ample buzz while in stealth mode.

Kammen sees Solyndra as a sign that the venture capital flowing into young solar companies the past few years is finally going to truly different ideas, not just refinements of older technology.

"A lot of smart money has gone into making better versions of existing stuff," Kammen said. "Now we're seeing a push to innovate."

Each of the company's cylinders is actually two glass tubes, one nested inside the other. Rather than silicon, the solar cells use a mixture of copper, indium, gallium and selenium deposited on the inner tube. The outer tube concentrates sunlight and protects the solar cells.

Solyndra's highly automated factory assembles the tubes and mounts them in panels, each containing 40 tubes. The panels are placed on racks that keep the tubes a few inches above the roof. The racks aren't bolted to the roof and can be quickly deployed or removed.

Company executives won't give exact prices but say the system's simplicity cuts the cost of installation in half. It also takes one-third as much time as it does to install a standard rooftop solar system, they say.

"It's just a couple of screws, and you hook it up," Gronet said.

Founded in 2005, Solyndra is growing quickly. The company already employs more than 500 people and plans to build a second, larger factory in Fremont. Its financial backers so far include CMEA Ventures, Madrone Capital Partners, Rockport Capital Partners and Virgin Green Fund.

E-mail David R. Baker at dbaker@sfchronicle.com.

This article appeared on page D - 1 of the San Francisco Chronicle