Thin Film to Outperfom Crystalline? Say What?

EETimes/R. Collin Johnson/Fenruary 3, 2009

PORTLAND, Ore. — Thin-film solar cells can use inexpensive, low-temperature processing to stack amorphous silicon and germanium photovoltaic layers atop a reflective foil backing. By using multiple layers with semiconductor junctions tuned to different wavelengths of light, thin-film module makers claim that their solar cells are not only cheaper, but could outperform expensive crystalline solar cells in many climates.

Advanced Green Technologies (AGT, Ft. Lauderdale, Fla.) claims its thin-film solar cell modules trade higher output on sunny days for better performance on cloudy days. AGT said its thin-film cells outperform glass encapsulated monocrystalline solar cells where sunny days are the exception. The reason, the company said, is that they continue to produce electricity when its cloudy.

"That trade-off is regional," said AGT's Gene Okun. "If you are in an area that has all sun, such as southern California, then very well we may find that the glass does produce more electricity than the thin film. In areas like Oregon and New Jersey and other northern regions where you have inclement weather a good majority of the year, our thin film will actually produce more power on an annual basis."

AGT uses flexible, lightweight laminates, encapsulated in a transparent, ultraviolet stabilized polymer, which it fabricates into large modules that are extremely lightweight compared to the glass-encapsulated modules used by crystalline solar cells.

"What we do is take the thin film [material] and create a 10- by 20-foot modules, which are then deployed on very large scale roofs--particularly roofs that are single ply and cannot maintain the weight load of heavier glass panels," said Okun.

AGT's modules use thin-film photovoltaic laminates manufactured by United Solar Ovonic, a subsidiary of Energy Conversion Devices Inc. (Rochester Hills, Mich.).

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