Global Solar scaling CIGS heights

by Katherine Derbyshire, Contributing Editor, Solid State Technology

Given the excitement surrounding the solar sector, it seems unlikely that a major solar cell supplier could remain below the radar, but Global Solar has. Part of the company’s low profile may have to do with its location in Tucson, far from the nurturing environs of Silicon Valley and Austin, TX, and the venture capitalists that have poured funds into companies like NanoSolar and HelioVolt. Part may stem from its longevity: the company was incorporated in 1996. By the time the current boom began, it was already old news.

And yet, unlike its flashier competitors, Global Solar’s products are fully commercialized and readily available. The company deposits CIGS (copper indium gallium diselenide) films on stainless steel foil, and supplies portable chargers for military, expedition, and other outdoor applications. When a climber on Mt. Everest calls home, there’s a good chance his satellite phone is powered by a Global Solar charger. For permanent installations, the company supplies “stringers,” square cells connected by silver tape that can be dropped directly into modules designed for crystalline silicon.

According to Tim Teich, VP for sales and marketing, such products taught the company a lot about durability and encapsulation. Barrier layers that work for amorphous silicon solar cells won’t work for CIGS, which is much less tolerant of water vapor. Adhesion on polyimide films tends to be poor, and is the reason why Global Solar uses steel foil substrates instead. With both problems nearing resolution, the company is now focusing on throughput and efficiency.

Global Solar aims to improve efficiency by 1%/year, and hopes to reach 14% average efficiency within five years. (Teich is highly skeptical of NanoSolar’s claim to have achieved that mark already.) To increase throughput, Global Solar is scaling up production. The Tucson plant should reach 40MW of capacity this year, with 30MW coming online in Berlin in 2009. For 2010, an additional building in Tucson can accommodate up to 100MW of production. Scaling up production will help bring costs down, Teich noted.

Though utility-driven solar farms consume large numbers of cells, Teich believes the rooftop solar market is more promising. Solar farms are a relatively unproductive use of land; economic considerations suggest they should be sited in remote areas where land is inexpensive. Yet transmission losses are one of the largest consumers of electrical power — fully 40% of all power generated is lost in the grid. Rooftop locations minimize transmission losses by putting the source of electricity close to the end user, and take advantage of space that would otherwise be wasted.

Teich also emphasized that installed cost matters more than cell cost. The current landscape, littered with custom module assemblers and small system installers, contributes enormous overhead to the total system cost. Reducing cell cost means nothing as long as the installed cost stays near $7/W. Development of standard building-integrateable products, such as architectural glass and solar roofing shingles, is one goal of Global’s recently announced partnership with Dow Chemical’s building solutions division. — K.D.


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