CaliSolar is close to raising more than $50 million to build a commercial plant in California next year, CEO Roy Johnson told Greentech Media this week.

Talks with investors are going well, Johnson said, adding that he expects the company’s second round of funding to close this summer. He declined to say exactly how much money CaliSolar seeks.

The two-year-old startup, based in Sunnyvale, Calif., raised $9 million from Advanced Technology Ventures and Globespan Capital Partners in 2006.

The company, which is developingsolarcells made with refined metallurgical silicon, has already built a pilot plant with a production capacity of 2 megawatts to 3 megawatts, Johnson said. He declined to provide details about the commercial plant, but said the company plans to release more information in the next few months.

“We are just now ramping up that pilot,” Johnson said. “We are doing thousands of solar cells a week and will be doing tens of thousands of cells in the next few months.”

CaliSolar is developing its technology based on research by cofounder Eicke Weber from when he was a materials science professor at the University of California at Berkeley. Weber is also chairman of Intersolar North America. The research studied ways to make solar cells from metallurgical silicon that has been upgraded, or purified.

Metallurgical silicon is less pure than the type of silicon that has traditionally been used to make solar cells and computer chips. But it’s much cheaper, making it an attractive raw material for the solar industry.

The challenge, though, is to refine the metallurgical silicon so that the cells made from it would have similar efficiency – measured by the percent of sunlight that they can convert into electricity – as those built with purer semiconductor-grade silicon.

Companies that use the solar-grade silicon also need to figure out how to tease the material into productive solar cells, which are then strung together into panels for residential and commercial installations.

Last month, CaliSolar named its first solar-grade silicon supplier – Bécancour Silicon, a subsidiary of Timminco in Toronto. According to the agreement, Bécancour Silicon plans to deliver 1,700 metric tons of solar-grade silicon from the third quarter of this year until the end of 2012.

Greentech Media caught up with Johnson to find out more about what CaliSolar is up to.

Q: Is CaliSolar on schedule with its solar-cell development?

A: We have done better than originally expected. We had an idea about how long it would take to make 15 percent cells, but we didn’t expect to get there this quickly. We are probably a year ahead.

Q: Have you lined up customers?

A: We have delivered cells to potential customers for evaluation, and we have gotten very good feedback. On the strength of our pilot plant, we believe we can convince people that we can deliver the right mechanical and electrical characteristics at the right price point and drive reasonable volume over the next six months. By the time we get the manufacturing plant up and running next year, we will already have contracts long sorted out.

Q: What are the price points and the manufacturing costs?

A: We are not talking about that. What I can say is our advantages will primarily be in our feedstock cost. In general, our process cost is not that different than what’s in the industry. We have developed the ability to get the higher efficiency and [to deal] with the impurities of the materials.

Q: Are you lining up other suppliers?

A: Nothing I can talk about.

Q: Although silicon is the main ingredient in most solar cells today, many companies are working on using different materials that would produce thinner and more flexible cells. Are you concerned about encroachment by the thin-film sector?

A: Thin-film is interesting. But as you know, the vast majority of the market today is crystalline silicon-based. There is plenty of room available for everybody. We don’t see a competition because the market growth will be so huge.

Q: Where is your primary market?

A: Our plan is to build our first manufacturing cell line in California because California and the southwest are hugely under-penetrated solar markets. Germany has done a good job of subsidizing the industry, but California has an opportunity to do better. We get twice the amount of sunshine as Germany does.

Q: You have a lot of experience in the networking industry. How does that help you run a solar startup?

A: It really doesn’t matter whether you are doing solar or networking. I am not in the company because I am a technologist. I am in the company because I ran companies before, so that’s really the key. One of the things I like about this industry is it’s growing so quickly, and it’s good for everybody.

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