World Record for Concentrator Photovoltaics
36.7 percent efficiency for module using highly efficient multi-junction solar cells
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have announced a world record efficiency of 36.7 percent for the Institute's concentrator photovoltaic (CPV) technology, which is the basis of the FLATCON module. The technology, which uses Fresnel lenses to collect sunlight and focus it onto miniature highly efficient solar cells, has been improved by adapting the concentrating lens to a new solar cell structure.
Key to this achievement was Soitec's four-junction solar cell based on wafer bonding technology and developed in cooperation with Fraunhofer ISE. This four-junction solar cell was implemented into the FLATCON module. The module aperture area, defined as the surface area of the module exposed to light, is 832 cm2. The sunlight is concentrated by a factor of 230 suns onto fifty-two 7 mm2 miniature solar cells with the help of fifty-two 16 cm2 Fresnel lenses.
The high module efficiency was measured under Concentrator Standard Testing Conditions, or CSTC, and marks the best value ever achieved for a photovoltaic module.
"Naturally we are incredibly excited about this high module efficiency," says Andreas Bett, who has led the CPV research at Fraunhofer ISE over many years. For his efforts Bett has received many awards, among them the German Environmental Award 2012, together with Hansjörg Lerchenmueller of Soitec Solar. "This success shows that the high efficiencies of Soitec's novel four-junction solar cells can be transferred to the module level."
Only several months ago, Fraunhofer ISE together with Soitec, the French research center CEA-Leti, and the Helmholtz Center in Berlin announced a new solar cell world record of 44.7 percent under concentrated light. This record cell consisted of four sub-cells made up of the compound semiconductors GaInP, GaAs, GaInAs and InP respectively. In comparison to standard silicon solar cells, the manufacture of four-junction solar cells is more expensive so that up to now their terrestrial applications have been exclusively in concentrator systems.
Concentrator photovoltaic systems (CPV) are installed in sun-rich regions, where such systems produce solar electricity for less than 8 eurocents per kilowatt-hour. Key to this technology is the solar cell efficiency and the concentrating optic. In the record module, the newly developed four-junction solar cell was combined with Fresnel lenses, which were manufactured by the industry partner ORAFOL Fresnel Optics based on a new design developed at Fraunhofer ISE. The successful transfer of this high module efficiency to commercially manufactured modules is expected within one to two years.
