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The impact of non-uniform illumination on triple junction solar cells equipped with either refractive or reflective optics without secondary optical elements is characterised by varying the concentrator-to-receiver distance. Indoor experiments covering both electrical measurements and photographs with a charge-coupled device camera are performed. The non-uniformities are examined by differentiating two spectral bands, those affecting the top and middle subcells. This allows the irradiance and spectral distributions to be analysed. The analysis is complemented with ray tracing simulations. Results show a different behaviour for the refractive and reflective systems. Irradiance non-uniformities in the case of the reflective system around the on-focus position are higher than those measured in the refractive system. However, the spectral non-uniformities that characterise the refractive system constitute only a residual effect in the reflective system. The drop in the solar cell fill factor caused by non-uniformities is mainly driven by the degradation of the slope of the I–V curve near the short-circuit point in the case of the refractive system, while it is mainly driven by the degradation of the slope of the I–V curve near the open-circuit point in the case of the reflective system. Both systems are very sensitive to the concentrator-to-receiver distance, a critical parameter that must be accurately designed in any concentrator system. The findings will allow the trade-off between increasing performance and increasing cost strategies to mitigate the non-uniformities in concentrator photovoltaic systems to be better evaluated. • Non-uniform illumination on triple-junction solar cell concentrators is analysed. • Refractive and reflective systems without secondary optics are characterised. • Concentrator-to-receiver distance is varied in simulations and experimentally. • Electrical measurements and charge-coupled device camera photographs are used. • Results will help the strategies to mitigate non-uniformities to be better evaluated. [ABSTRACT FROM AUTHOR]

Non-uniformity is a relevant concern of concentrator photovoltaic systems (CPV) due to its impact on the performance of multi-junction (MJ) solar cells. This work is focused on a state-of-the-art investigation related to the effects of shading on the irradiance profiles and electrical performance of MJ cells. For doing this, three different CPV single-units with a concentration of ≈559x have been experimentally investigated indoors at the CPV laboratory of the University of Jaén. The units are made up of poly(methyl methacrylate) (PMMA) Fresnel lens and standard GaInP/GaInAs/Ge MJ cells. Also, single-lens-optical element (SILO-Pyramid) and refractive truncated pyramid (RTP) homogenizers have been considered. The results indicate that shading produces additional spatial and spectral non-uniformities, and that these are reduced by the use of homogenizers. In addition, the non-uniform spectral illumination has been identified as the main cause of the additional reduction of the performance of MJ solar cells. In this sense, the SILO-Pyramid provides the best results and shows a significantly stable spectral performance under shading conditions. For a no-homogenizer case, the maximum power shows a reduction of 86.3% for a shading factor of 80%, while it is only reduced by 83.2% and by 81.6%, respectively, for the RTP and SILO-Pyramid. • Non-uniformity on multi-junction solar cell caused by shading is investigated. • Different types of refractive homogenizers are considered. • Shading is produced on the surface of a Fresnel lens by using opaque masks. • Electrical measurements and charge-coupled device camera photographs are used. • Results will help to propose strategies to mitigate non-uniformities under shading. [ABSTRACT FROM AUTHOR]