Suniva announced Thursday that it has begun building its first factory, which is expected to start producing silicon-basedsolarcells during the fourth quarter. And, the company is already in the process of lining up its first three customers.

The startup said it is retrofitting a warehouse to develop its first factory on a 73,000-square-foot property in Gwinnett County, Georgia, near the company’s Atlanta headquarters.

Suniva plans to spend $75 million over the next few years in order to manufacture more than 100 megawatts of cells, Suniva CEO John Baumstark said.

He told Greentech Media that the company is negotiating contracts with three international customers and hopes to reveal the buyers in July.

The near-term plan is to install a 32-megawatt production line by the end of this year. Suniva will then join a host of companies worldwide in a race to roll out cheaper and more efficient silicon solar cells.

The company, a spinoff of the Georgia Institute of Technology, said it’s found a secret sauce to squeeze more electric power out of its solar cells while pushing down the manufacturing cost.

The company has yet to provide much evidence to back up the claim, but has said that its solar cells can convert 18 percent of the sunlight that hits them into electricity.

It’s an attractive number. But SunPower (NASD: SPWR), a solar panel maker that also develops its own cell technology, said in May that its engineers had created a prototype cell with a conversion efficiency of 23.4 percent. The company then began selling panels using cells with 22-percent efficiencies.

Baumstark said he isn’t worried. “We feel comfortable with our competitiveness,” he said. “We can make highly superefficient cells and make them at a low cost.” But Baumstark declined to say how low.

Travis Bradford, president of the Prometheus Institute, a Greentech Media partner, has forecast that solar-panel manufacturers would have to be able to make money at prices of less than $2 per watt by the end of 2010 to remain competitive, suggesting that Suniva’s cell prices would have to be lower than that (see Solar Sector Heading for a Shakeout).

But manufacturing is a game of scale, and Suniva is up against much larger competitors, such as Q-Cells in Germany and Sharp in Japan.

Still, some investors apparently think the startup has a chance. Suniva raised a second round of funding of $50 million in February, bringing the total investment in the company to $55.5 million since its inception in 2006 (see Solar Startup Suniva Snags $50M).