Researchers develop low-cost technique to double solar energy news
05 November 2012

In order to enhance solar energy's potential, Andreas Bett of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg and Hansjörg Lerchenmüller, general manager of Soitec solar GmbH have developed concentrator photovoltaic systems based on multijunction solar cells, and deployed them for industrial use.

This effectively makes photovoltaic technology even more efficient and more affordable, an achievement for which the two innovators were awarded Germany's most highly-endowed award 2012 DBU German Environmental Award (DBU Deutscher Umweltpreis), that offers € 500,000

This system is capable of converting almost twice the available sunlight into electricity as compared to conventional silicon-based systems.

Yet how does one manage to double power output using multi-junction solar cells? Conventional solar cells made of silicon are unable to convert the entire solar spectrum into power.

The two experts in photovoltaics therefore used an array of different semi-conducting materials. They stacked layers of gallium indium phosphide, gallium indium arsenide and germanium in layers, which allows them to capture the sun's almost entire energy.

Three years ago, the research team under Bett achieved a degree of efficiency equal to 41.1 per cent – a world record at the time.

It costs a lot of time and money to produce triple-junction solar cells. So, to make multi-junction solar cells affordable, the researchers resorted to a trick. They put a lens in front of each cell, which then bundles the sunlight 500-fold. The tiny semiconductors, measuring a mere three millimeters in diameter, are now sufficient enough to catch focused beams of light.

''The use of low-cost focusing optics fosters an economical use of otherwise expensive semiconducting materials," explains Dr. Bett, division director of Materials – Solar Cells and Technologies, and deputy director of Fraunhofer ISE. "Depending on the concentration factor, you only need one five-hundredth to one one-thousandth of the semiconducting material – but you can still elevate the efficiency of the solar cell.''

Increased efficiency of multi-junction solar cells
Together with his colleagues at Fraunhofer ISE, Bett succeeded in improving the efficiency of multi-junction solar cells and in optimising the development of the concentrator photovoltaic module.

The Concentrix Company was founded in 2005 in Freiburg to facilitate its industrial application. Four years later, Soitec acquired the spin-off company. Hansjörg Lerchenmüller, a former colleague at Fraunhofer ISE, advanced the commercialisation and internationalisation even further, ever since the spin-off. Soitec successfully brought the design of the concentrator photovoltaic module to serial production, and today it is the global market leader. Industrially manufactured modules have a 30 per cent degree of efficiency: a value that Lerchenmüller and Bett intend to increase over the coming years.

The concentrator photovoltaic modules require direct solar radiation. They are therefore particularly suited for use in solar parks in South Europe, North Africa, the American Southwest or the Middle East. The Soitec Company's solar power plants – which have a total capacity in excess of 10 megawatts – already operate in 14 different countries.





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Researchers develop low-cost technique to double solar energy