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Winter 2008

New Copper Solar Cells Promise a Bright Future

High-resolution version of this photo.

Renewable energy is the hottest topic in energy circles these days. It refers to "green" energy sources like plant-based biofuels that can be regenerated, as well as natural sources such as wind, hydro, geothermal and solar power, which can't be depleted.

Using renewables in place of carbon-based fuels such as oil and gas offers obvious environmental and even political advantages. However, most of these alternative energy sources are still in development and require subsidies or incentives to become practical. In the case of solar electrical generation, the economics have actually gotten worse, although this situation is poised for a significant turnaround.

Copper and its alloys are vital to energy production, including renewable energy. Copper provides both high heat-transfer capability and superior electrical conductivity, helping to increase the efficiency of all types of systems, from direct-exchange geothermal heat pumps for home heating to today's high-tech, high-megawatt wind farms.

Solar hot-water systems, which typically include copper tubing and heat exchangers, are familiar to many homeowners. Less well known is that copper is becoming equally valuable in solar-electrical, or photovoltaic (PV) systems. These systems convert sunlight to electricity through silicone-based semiconductors and thin-film materials such as cadmium telluride and gallium arsenide. But the most promising energy-generating material on our solar horizon is copper-indium-gallium-diselenide, or CIGS. A CIGS cell holds the record for the total percentage of energy converted (19.5%) from direct sunlight.

Despite today's explosive growth in solar power, and increased production of solar cells, the cost of PV power remains high-and continues to rise due to a worldwide shortage of cell-grade silicon. This is where CIGS offers an important advantage. Compared to silicon, which requires multiple manufacturing steps before the material is shaped into individual cell wafers, the CIGS process is relatively energy-efficient, and its technology has advanced to a point where the material can now be deposited as a "coating" on inexpensive strips of material.

According to Scott Albright, director of Advance Programs for Global Solar, located in Tucson, Arizona, CIGS is now cost-competitive with silicon. "And," he adds, "unit costs will continue to decrease as we begin to take advantage of economies of scale." Like other CIGS producers, Global Solar is currently expanding its facilities to increase output-the factory here that produced the equivalent of four megawatts (MW/y) of solar units per year will churn out more than 40 MW/y in 2008. The company, which is owned in part by German solar module manufacturer Solon AG, is also expanding its manufacturing operations in Germany.

Industry news service notes that a number of companies are currently producing or ramping up to produce CIGS. Global Solar is a leader in CIGS production technology. The company developed an efficient film deposition process that has since become a commercial standard, enabling lower manufacturing costs and faster production than the batch operations formerly used in semiconductor manufacture.


Global Solar is also the world's leading flexible PV supplier. These lightweight, portable modules were first adopted by U.S. and foreign armed forces, which needed a reliable power source for the many electronic devices employed by today's high-tech troops. The company has also created a line of innovative solar products used by outdoor enthusiasts and scientific researchers worldwide.

Also in development are rigid, panel-mounted modules suitable for commercial solar farms and home installations. Utilities foresee numerous small solar installations that can be located where energy is needed, as a way to more efficiently distribute electrical power. "That technology is coming," says Albright, "and that's where we believe a really significant amount of solar utilization will develop."


CIGS moduleThis is not a staged picture! A scientist working in Antarctica needed an environmentally nonintrusive power source to recharge his PDA and laptop batteries. One of Global Solar's portable CIGS modules provided the "green" solution.

Photo courtesy Global Solar Inc.

The CIGS material in a solar cell is only a few microns thick, and the copper in it makes up only a fraction of its weight. But, it is critical to the performance of the cell. Also, when distributed solar power attains the scale Albright envisions, it will require miles of copper cables, not to mention copper-wound transformers, inverters and switchgear to ensure maximum efficiency.

And that's just for the power equipment. Electrical installations must be grounded, and here, again, the superior conductivity of copper will undoubtedly be significant. Only copper cables and connectors provide the reliability these systems demand.

Globally, the solar industry is currently growing at a 34% compounded annual rate. If solar energy's time has finally come, as Scott Albright along with many industrialists and economists now believe, it is certain that the environment, assisted by copper, has a bright future. Cu

This article was adapted from a technical casestudy posted on the Copper Development Association Web site. For the complete version, see: Copper-based Solar Cells


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