The Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany has achieved record photovoltaic (PV) solar module efficiency of 36.7%, as measured under Concentrator Standard Testing Conditions (CSTC). This has been done by adapting the concentrating lens to a new solar cell structure.
Fraunhofer ISE has been developing concentrator photovoltaic (CPV) technology for many years, using Fresnel lenses to focus sunlight onto multi-junction solar cells. The institute originated the FLATCON module technology and is continually developing it, leading to the new record.
Decisive in the latest achievement was the newly developed four-junction solar cell of CPV solar system maker Soitec of Bernin, France, which is based on wafer bonding technology and developed in cooperation with Fraunhofer ISE. This four-junction solar cell was recently implemented into the institute’s FLATCON module concept. The module aperture area (the surface area exposed to light) is 832cm2. Light is concentrated by a factor of 230 suns onto 52 7mm2 miniature solar cells with the help of 52 16cm2 Fresnel lenses.
Picture: Fraunhofer ISE‘s latest, 36.7%-efficient FLATCON CPV module. Fraunhofer ISE/Photo: Alexander Wekkeli
“This success shows that the high efficiencies of Soitec’s novel four-junction solar cells can be transferred to the module level,” says Dr Andreas Bett, who has led the CPV research at Fraunhofer ISE over many years. For his efforts, Bett has received many awards, including the German Environmental Award 2012 (together with Hansjrg Lerchenmüller of Soitec Solar).
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 efficiency record of 44.7% under concentrated light. This cell consisted of four sub-cells consisting of gallium indium phosphide (GaInP), gallium arsenide (GaAs), indium gallium arsenide (GaInAs) and indium phosphide (InP), respectively. Compared with standard silicon solar cells, the manufacture of four-junction solar cells is more expensive, so up to now their terrestrial applications have been exclusively in concentrator systems. Also, CPV systems are installed in sun-rich regions, where such systems can produce solar electricity for less than 8 eurocents per kilowatt-hour.
Key to this technology is the solar cell efficiency and the concentrating optics. In the record module, the new four-junction solar cell was combined with Fresnel lenses manufactured by industry partner ORAFOL Fresnel Optics GmbH of Apolda Germany, based on a new design developed at Fraunhofer ISE. Transfer of this high module efficiency to commercially manufactured modules is expected within 1-2 years.
