Spectrolab is a unit of Hughes Electronics Corp. The cell is Spectrolab's triple-junction gallium-indium-phosphide on gallium arsenide on germanium (GaInP2/GaAs/Ge) concentrator solar cell.

"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 added. "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 measurement for the world record was made under an Air Mass 1.5 direct spectrum (AM1.5D), the spectrum typically used to measure concentrator cell performance in terrestrial energy generation systems. The data was recorded by NREL on a device structure grown by Spectrolab and processed and measured at NREL. The measurements were performed at various concentration ratios between 1X and about 300X. The cell performance peaked at a concentration of approximately 50 suns.

Dr. Jerry Olson, principal scientist in the High-Efficiency and Concentrators Photovoltaics Group at NREL, said: "I am very pleased to see industry beginning to take GaAs-based cells seriously for terrestrial power generation. This is a very encouraging result, and is supportive of the Department of Energy's 'One-Third of a Sun' initiative to develop solar cells that convert one-third or more of the sun's energy to electricity.

"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."

There is considerable synergy between space and terrestrial cells. In addition, the efficiency improvements for terrestrial cells are expected to be driven by improvements in space cells. During the last few years, multi-junction solar cells have doubled the power output of large commercial satellites, and substantially improved their revenue-generating capability.

A nearly 40% conversion efficiency has been forecast for four-junction space solar cells, currently being developed under a Dual Use Science & Technology program jointly funded by Spectrolab and the government. Similar cells, optimized for terrestrial use, have the potential to surpass 40% conversion efficiency.

Terrestrial solar cells will also be the driving force to reduce the cost of materials used in space and terrestrial applications. This will add to the economic attractiveness of GaAs-based technology for large-scale utility energy generation.

A significant advantage of concentrator systems lies in the fact that fewer solar cells are required for a given module power output, since the semiconductor portion is replaced with relatively inexpensive optics that provide optical concentration. Because fewer cells are required, concentrator systems can afford the slightly higher cost of multi-junction cells, and yet still be manufactured at lower dollar-per-watt cost compared to other flat-plate modules.

Due to the higher efficiency of multi-junction cells used in the concentrator modules, only about one-half of the real estate is required to generate the same power output compared to crystalline silicon or thin-film flat-plate modules.

NREL is the U.S. Department of Energy's premier laboratory for renewable energy and energy-efficient research, development and deployment.

Spectrolab, founded in 1956, has been supplying solar cells and panels to the space industry for 40 years. Pioneer 1, launched in 1958, carried the first body-mounted panels used in space. The following year, Explorer 6 used Spectrolab products and was the first satellite to use solar arrays instead of body-mounted panels.

National Renewable Energy Laboratory

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