GT's based in New England and actually builds equipment there. That's turning out equipment needed to make multi-crystalline solar wafers, cells and modules. All of which is used in the photovoltaic industry. GT also sells polysilicon reactors needed to produce the polysilicon from which solar wafers are fabricated. GT is not just in the U.S. Last year they opened the first solar plant in the Netherlands.
From GT's self-description: "The company’s revenues have risen from that first order of $220,000 in 1994 to more than $58 million in fiscal 2006. Over 85% of the company’s shipments are exported to countries around the world such as Germany, Spain, China, Taiwan, and Korea. And, the company is expanding its facility on some of the 14 acres. In 2006, two investor groups – GFI Energy Ventures, LLC and the Angeleno Group –acquired a majority interest in the company."