Researchers from the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany have used their concentrator photovoltaic (CPV) technology to set a new world record for the efficiency of solar cells. The CPV system, which uses Fresnel lenses together with multi-junction solar cells, achieved a module efficiency of 36.7 per cent, and is expected to be used in commercially manufactured systems within the next one to two years.
To achieve such a high efficiency, the ISE team used new four-junction solar cells from French company Soitec, which are based on wafer bonding technology developed in cooperation with Fraunhofer ISE. Only a few months ago, this four junction cell achieved a solar cell world record of 44.7 per cent efficiency under concentrated light.
The solar module consists of four sub-cells made up of the compound semiconductors GaInP, GaAs, GaInAs and InP. 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.
More recently, the Fraunhofer researchers were able to implement the four-junction solar cell into the institute’s Flatcon module concept, where Fresnal lenses are used to concentrate and focus the sunlight onto the solar cells.
The combination of the four-junction solar cell with the concentrating optics − the Fresnal lenses − was key to achieving the high efficiency. The lenses were manufactured by industry partner Orafol Fresnel Optics based on a new design developed at Fraunhofer ISE.
The Flatcon modules surface area − the surface area of the module exposed to light − is 832cm², and by using 52 16cm² Fresnal lenses, sunlight shining on this surface area is concentrated to a factor of up to 230 suns onto 52 7mm² miniature solar cells.
‘Naturally we are incredibly excited about this high module efficiency,’ said Dr Andreas Bett, who led the CPV research at Fraunhofer ISE. ‘This success shows that the high efficiencies of Soitec’s novel four-junction solar cells can be transferred to the module level.’
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