This paper describes an approach of making the FLATCON® CPV technology compatible with standard photovoltaic simulation software like PVSYST and INSEL in order to facilitate yield estimations for potential power plant sites. Due to the use of triple-junction cells, the FLATCON® CPV module efficiency is more sensitive to changes in the solar spectrum than the efficiency of an average single-junction flat plate module. Besides that, the concentrating optics show a temperature dependency. These effects result in a non-linear component in the short circuit dependency on the direct normal irradiance. By means of introducing a "Utilization Factor", deduced from both measured data and theoretical considerations, these CPV peculiarities can be considered in standard software tools and transferred to other locations without the need of overly complex measurements or algorithms.

In this paper we report on research activities at the Fraunhofer Institute for Solar Energy Systems (ISE) and Concentrix Solar in the area of secondary optics for FLATCON ® modules. This concentrator photovoltaic (CPV) technology is based on Fresnel-lenses as primary optics, passive heat spreaders and triple-junction III-V solar cells. In the first part of the paper, a field performance analysis is presented for Concentrix CPVsystems recently installed in Spain. Subsequently, the performance of the first FLATCON ® modules with reflective and refractive secondaries are evaluated (FLATCON ® II) in indoor and outdoor measurements. As a result of this development, the first module with automated assembly process of the secondary optics could be manufactured. The highest outdoor efficiency measured for this kind of module is 29.1 %, which is the highest module efficiency achieved at the Fraunhofer ISE so far.

AlGaAs/GaAs heteroface solar cells with a high aluminium content tend to degrade. The degradation mechanism has been examined and appropriate accelerated ageing procedures have been established. They effectively test the ruggedness of the device against oxidation. Changing the window layer material to (Al(ind x)Ga(ind 1-x))(ind 0.51)In(ind 0.49)P with x = 0, 0.5 or 1 leads to stable devices. In addition, III-V tandem solar cells for concentrator applications were subjected to accelerated ageing tests. They proved to be robust against oxidation. The potential degradation due to the high current density involved in concentrator solar cells was assessed in preliminary experiments

Abstract. CPV systems using 3-junction solar cells have proven good performance and reliability. As the performance of 3-junction cells is saturating [1], the logical next step is the introduction of 4-junction (4-J) solar cells into CPV modules. The current world record for cell efficiency under concentrated light of 46.0% was achieved using a wafer bonded Soitec 4-J cell (SmartCell TM ) [1][2][3][4]. This paper discusses a new module design, optimized for harvesting the full potential provided by this high cell efficiency. Prototype modules have been built in order to explore the design space. A module efficiency of 38.9% under concentrator standard test conditions has been achieved.