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Photovoltaic (PV) waste, associated to the exponentially growing PV installations on global scale, presents today an emerging environmental challenge but also brings unprecedented and multifold value creation opportunities. In this context, significant PV business and research and development (R&D) efforts shift towards establishing a more sustainable, environmentally friendly and economically viable end-of-life (EoL) management for PV modules: including recycling, recovery of raw materials, repair/refurbishment and even re-use of decommissioned or failed PV modules. In the CIRCUSOL project, PV partners aspire to formalize the repair/refurbish and reuse value chains in the PV industry and propose a circular business model, based on a product-service system (PSS). Towards these goals, this review study introduces the relevant research groundwork, a status overview and today's R&D and business challenges in PV recycling, repair/refurbishment and re-certification aspects for second-life PV modules. The topics and the relevant reported literature are examined from both circular economy and technology perspective. The review indicates a considerable technological and operational know-how in PV EoL management that already exists and continuously evolves in mature PV markets. On the other hand, R&D in repair/refurbishment of decommissioned and/or failed PV modules remains scarce, and best practices and commercial services for reliability testing/recertification and trading of second-life PV modules are neither standardized nor consolidated into any PSS or business model.

Today, conventional condition monitoring of installed, operating photovoltaic (PV) modules is mainly based on electrical measurements and performance evaluation. However, such practices exhibit restricted fault-detection ability. This study proposes the use of standard thermal image processing and the Canny edge detection operator as diagnostic tools for module-related faults that lead to hot-spot heating effects. The intended techniques were applied on thermal images of defective PV modules, from several field infrared thermographic measurements conducted during this study. The whole approach provided promising results with the detection of hot-spot formations that were diagnosed to specific defective cells in each inspected module. These evolving hot spots lead to abnormally low performance of the PV modules, a fact that is also validated by the manufacturer's standard electrical tests.

The combination of increasing operational voltages beyond 1000 V in photovoltaic (PV) installations and the emergence of new PV technologies requires a critical assessment of the susceptibility to potential-induced degradation (PID). Since this failure mode can trigger significant and rapid power losses, it is considered among the most critical failure modes with a high financial impact. Insights in the physical mechanism of the performance loss and its driving factors are critical to develop adapted characterization methods and mitigation solutions. PID in p-type solar cells is triggered by sodium (Na) that diffuses into stacking faults of the silicon lattice, causing shunt paths through the pn-junction. In addition, it is hypothesised that for bifacial p-PERC solar cells positive charges, such as Na + , accumulate in/on the negatively charged AlO x rear passivation layer due to the potential difference between the glass and the rear cell surface. This significantly increases surface recombination. However, the degradation behaviour observed in bifacial monocrystalline p-PERC solar cells under PID stress from both sides (bifacial PID stress) does not match with just one of the degradation mechanisms. A comprehensive test matrix was carried out to understand the physical origin of PID in front emitter bifacial p-PERC solar cells in a glass/glass packaging. The results show that bifacial p-PERC solar cells under bifacial PID stress suffer from both shunting of the pn-junction and increased surface recombination at their rear side. Hereby, we prove that the glass/glass packaging in combination with bifacial solar cells can significantly increase the severity of PID.

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