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Commercial rooftops sporting solar panels are becoming a familiar sight. But the technology used is still changing, with companies like thin-film panel maker Xunlight working to change the way big box retailers and others get their solar energy.

Xunlight has just received an additional $7 million in a loan from the state of Ohio, where the company is based, to speed work on a 25 megawatt production line in Toledo. The facility should be done next year, making flexible, lightweight panels that can be laid atop wide, flat rooftops like a carpet.

So far, there aren’t any major installations of thin-film panels on commercial roofs because the technology is still under development. The regular silicon photovoltaics that companies like Wal-Mart are placing atop their stores do the same job, but thin-film makers argue that their panels are much better, because they don’t require heavy racking systems that keep them angled toward the sun.

Because thin-film panels are cheap and low-efficiency, they can be laid flat, and cover almost all available space. And even when compared to a regular silicon panel, not including the rack, they’re still much lighter and easier to place.

After finishing its first manufacturing line and starting production early in the third quarter of 2009, Xunlight will work on ramping up with the aim of reaching 150MW of capacity by the end of 2010, according to company spokesman Todd Armstrong.

Xunlight uses an amorphous silicon technology for its panels, with which it hopes to average 8 percent efficiency. However, although there is very little thin-film on commercial rooftops today, it won’t lack for competition from companies with slightly different technologies. Nanosolar has also expressed interest in the market, along with Lumeta, Uni-solar and Solyndra, which just raised $600 million.

The $7 million loan Xunlight took came from an Ohio R&D development fund and a bond fund. The company has also taken several other rounds of funding this year, including $22 million in April, another $11 million in August and a $4.9 million state grant in July.

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