June 1999

Copper Increases Efficiency of Solar Cells

Copper Applications in Health & Environment


As if designed as an element in a futuristic novel, the Siemens Solar Group has used copper to design an environmentally friendly, solar-energy product that will provide power to the people of the 21st Century.

The energy contained in the sunlight hitting the Earth each day is far greater than that generated by the human race by burning coal, oil, or nuclear power. Photovoltaic solar cells use the sunlight to generate electricity. They are quiet, give off no pollution, do not require much land and water to operate, and can be used to generate both electricity and fuels.

Siemens Solar is the world's leading manufacturer in the photovoltaic industry. Working with the assistance of experts from several countries, Siemens is trying to use sunlight, along with another resource that is in abundant supply: copper, to power the future.

In the past, it has been more expensive to convert solar energy to electricity, as compared to other more readily available energy sources. But thanks to the joint effects of Siemens Solar GmbH in Munich, Germany (a joint venture of Siemens AG and Bayernwerk AG); Siemens Solar Industries, a limited partnership in Camarillo, California; and two joint ventures, Siemens Showa Solar Ltd. In Singapore, and Showa Solar Energy K.K. in Tokyo, Japan; working together with the U.S. Department of Energy's (DOE) Thin-film Photovoltaics Partnership Program, a new breakthrough could make solar power more plentiful and inexpensive.

This group of professionals have set about testing the capabilities of a new thin-film photovoltaic module that is created by applying a fine film of copper indium diselenide (CIS) to a glass backing - producing a semi-conductor. When the semi-conductor is exposed to sunlight, it actively converts sunlight into electricity - at a cost up to 10 times less than the crystalline silicon based cells now on the market.

This record setting one-foot by four-foot module was developed in collaboration with U.S. Government's National Renewable Energy Laboratory (NREL). Record breaking efficiencies of more than 12 percent have been confirmed for this new thin-film module - Siemens Solar ST40 large-area copper indium diselenide (CIS) photovoltaic (PV) product. Siemens has also begun research and development on a new module that combines amorphous silicon with CIS to create a double-layered thin-film that has a conversion efficiency of 15.6 percent. Amorphous silicon, which powers small solar devices, makes up more than 30 percent of all the photovoltaic power generated in the world. But this material also has a flaw that causes it to lose efficiency upon exposure. Layering this material with CIS might help eliminate this efficiency flaw. This double layering is also being tried with a variety of other materials to achieve higher performance at a lower cost.

"The increased efficiencies in solar technology brings us one step closer to the goal of developing this renewable energy resource for practical use in our everyday lives," said Energy Secretary Bill Richardson.

The joint effort between the DOE and Siemens Solar marks a partnership that is working to supply energy for the future while keeping an eye on environmental concerns. After testing at the NREL Outdoor Test Facility in Golden, Colorado, the array's efficiency has proved to be 40 percent above the closest thin-film contender, while all modules surpassed the 10 percent DOE year 2000 goal for commercial CIS modules.

"This is an important research milestone and a stunning achievement," James Rannels, Acting Director, Office of PV and Wind Technology, DOE, said.

While Siemens Solar produces a large product line of solar modules, the ST40 is for higher power applications. Other Siemens modules are ideally suited for low power battery-charging applications, such as in emergency telephones or telemetry systems, but higher power modules like the copper indium diselenide modules can be used in large grid-connected systems. This CIS technology can be applied in applications where options were formerly limited to crystalline silicon. The efficiency of these CIS modules has opened doors to a variety of new uses. For instance, the matte-black CIS solar module distinctive appearance makes it visually striking in architectural applications, opening up new possibilities for architects and designers of PV systems that are incorporated into building facades.

The production of these new photovoltaic cells will provide a cost-effective product that will make solar power cost effective for many new applications. In these times of political instability, there are stable supplies of energy readily available from the sun. This goal can only be achieved by transferring the technology from the lab to the factory for mass production - causing the cost of solar energy to be greatly reduced and opening the door for anyone to use this technology in the 21st century.

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