BioSolar said Tuesday it has developed a protective backing forsolarcells that is made of material derived from cotton and castor beans.

Founded in 2006, the Santa Clarita, Calif.-based company had previously said it was working on a bio-based “back sheet” for solar cells, but had kept all the details secret until now (see Creating a Solar Bond That Lasts).

With patents in place, Lee said the company was ready to divulge more about its first product. 

At a solar conference in San Diego, Calif., BioSolar said the sheet is meant to be an alternative to Tedlar, a petroleum-based film made by DuPont that most silicon-based solar-cell manufacturers use today.

BioSolar CEO David Lee claims the bio-sheet is more environmentally sound than Tedlar and also will sell for at least 25 percent less. Back sheets range from 70 cents to $1 per square foot today, Lee said.

The sheet consists of a mixture of cotton and a nylon resin that French chemical company Arkema makes from castor beans.

The tough part was figuring out how much cotton and resin to use, and how to combine them. It might sound simple, Lee said, but it's not. "The processing has to be done in a certain way" to get the two materials to stick together to form a protective barrier, he said.

Wallingford, Conn.-based plastic manufacturer Rowland Technologies has signed a deal to make BioSolar's BioBacksheet, Lee said.

But while the sheets the company has made in labs have performed well in tests, the company will have to conduct more tests once Rowland produces the first sheets to make sure commercial ones will perform as well, Lee said.

He also expects potential customers will want to test the back sheet on their own.

Lee said BioSolar, which is traded over the counter under the ticker symbol “BSRC,” is raising money through a private stock offering. He wouldn’t disclose how much it plans to raise or when he expects the company to close the funding.

In total, BioSolar has raised about $3 million from angel investors and its public offering in 2007.

Lee also said BioSolar won't need another cash injection until next year, when the company plans to ramp up production.