The global solar market has grown by about 40 percent annually for the past five years, driven largely by Germany and Japan, which rank Nos. 1 and 2 in the world in installed photovoltaics. The United States' 9 percent slice of the market ranks third.

New U.S. solar capacity increased to 927 megawatts (MW) in 2004, up 62 percent from 2003, according to Solarbuzz, a San Francisco-based industry research and consulting company. The industry, however, faces difficulties finding the raw materials needed to match that growth in 2005.

Manufacturers produce about 13,500 metric tons of solar-grade silicon annually. In 2005, the amount of silicon going into solar applications is projected to permanently outstrip the silicon going into computers, noted Washington State University's Nelson.

The net effect is a shortage of high-quality silicon, added Nelson. Installers worldwide are reporting months-long back orders and retailers are snapping up supply lines with vendors.

Issaquah, Wash.-based Costco Wholesale Corp. (Nasdaq: COST) has been selling small-scale solar kits online for two years. Strong sales of the 45- to 100-watt solar kits - particularly in the West and Southwest - are spurring the wholesaler to add a third vendor to its list of suppliers, said Chris Taylor, a Costco assistant buyer. And in spring 2006, the company's Web site will also feature 400-watt wind turbines designed for homes.

"These are products that fit our customer base — people who have RVs, trailers, boats, cabins and lake homes," Taylor added. "These people want products to take care of their toys."

Other big-box retailers are chasing after the same market. The Home Depot (NYSE: HD) sells 5-watt solar panel kits for automatic gate openers, and Wal-Mart (NYSE: WMT) sells solar battery-powered lights for yards.

Silicon certainly sells. But with a scarcity of the solar-grade variety, manufacturers are searching for cheaper and more-efficient substitutes.