CaliSolar, which is developing solar cells from a new breed of silicon, has raised $101.9 million.

CaliSolar CEO Roy Johnson told Greentech Media in July that the company was close to raising more than $50 million to build a commercial plant in California next year (see Q&A: CaliSolar Seeks $50M to Build Plant).

The Sunnyvale, Calif.-based startup has yet to discuss the new funding, which Private Equity Hub uncovered in a filing with the U.S. Securities and Exchange Commission.

The filing showed that CaliSolar had raised $51.9 million in a Series B preferred stock funding and another $50 million in convertible securities. Hudson Clean Energy led the round, and other investors included Advanced Technology Ventures and Globespan Capital Partners.

CaliSolar had previously raised $9 million from Advanced Technology Ventures and Globespan Capital Partners in 2006, when the company was founded.

CaliSolar, which has a development center in Berlin, is engineering solar cells made with upgraded metallurgical-grade silicon, also known as UMG silicon. UMG silicon is dirtier than the silicon used for producing most of the solar cells and compute chips today. The company has a pilot plant with a production capacity of 2 megawatts to 3 megawatts.

But metallurgical-grade silicon is much cheaper, making it an attractive raw material for the solar industry, which has had to compete with the chip industry for silicon supplies. Johnson told Greentech Media earlier this year that the cost of producing UMG silicon could be one-sixth that of making the purer silicon (see Charting a Path to Low-Cost Solar).

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 silicon.

In June, CaliSolar named Bécancour Silicon, a subsidiary of Timminco in Toronto, as its first supplier of the UMG silicon. Bécancour will deliver the silicon through 2012 as part of the deal.

Timminco (TSX: TIM) also has deals to supply silicon to Canadian Solar and Germany's Q-Cells, the world's largest solar cell maker (see Timminco Shares Down Despite Deal with Canadian Solar).

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