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Solar cell efficiency makes big leaps

October 27, 1999
Web posted at: 12:25 p.m. EDT (1625 GMT)

Testing a condensed solar cell.
Jerry Olson and Sarah Kurtz test an early version of the concentrator solar cell.  
By Environmental News Network staff

Terrestrial solar cell efficiency has taken another leap forward, converting a record 32.3 percent of the sun's energy into useable power more than doubling current efficiency ratings.

The milestone was reached by scientists at Spectrolab, a unit of Hughes Electronics Corp., and the Department of Energy National Renewable Energy Laboratory. The scientists believe they can take solar-cell efficiency to greater than 40 percent.

Terrestrial solar cells, those used on land as opposed to in space, have experienced several similar leaps in efficiency over the past few years thanks to technological advances that have been fueled by work in the space industry.

The new technology is called triple-junction gallium-indium-phosphide on gallium arsenide on germanium concentrator solar cell. Spectrolab has been working on different versions of this technology for more than 10 years. They have been able to steadily improve the efficiency of the solar cells since 1994.

Four-junction solar cells are being developed for the space industry right now and it will be this technology that takes terrestrial solar cells over the 40 percent efficiency level, according to Spectrolab.

"We are extremely excited about this result," said Dr. David Lillington, vice president for solid-state products at Spectrolab. "Multi-junction solar cells have made a major impact on the cost-effectiveness and revenue-generating capabilities of high-power space satellites over the last five years, and we expect them to have a similar impact on the $1 billion terrestrial photovoltaics industry.

"We have taken the basic cell design concept and made it cost-effective for terrestrial applications when it is combined with a concentrator system. By doubling the power generating efficiency of the cell, the size of the solar ray collection system can be reduced in half, thereby reducing the overall cost of the infrastructure," said Lillington.

"We are anxious to see the near-term deployment of our technology into large photovoltaic systems and are in the process of selecting industry partners with demonstrated field experience," he said. "The potential cost reductions are consistent with prices paid by utility companies for renewable energy sources such as silicon solar cells, wind generation and geothermal. No other family of solar cells offers the same opportunity to achieve such high performance."

"The challenge will now be for industry and government to work together to get these cells into real-life power-generating systems to validate their reliability and ability to last for long periods of use in the field," said Dr. Jerry Olson, principal scientist in the High-Efficiency and Concentrators Photovoltaics Group at NREL.

The concentrator system gains its advantage over traditional silicon solar cells by replacing the semiconductor portion with inexpensive optics (that provide optical concentration). Because fewer cells are required, concentrator systems can afford the slightly higher cost of high-efficiency multi-junction cells, yet can still be manufactured at a lower cost when compared to traditional solar cells.

Because the multi-junction cells are more efficient, only about one-half of the real estate is require to generate the same power output compared to crystalline silicon or thin-film flat-plate modules, according to Spectrolab.

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Hughes Electronics
National Renewable Energy Laboratory
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