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.
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.
Highlights• MoOx is used to replace p-a-Si:H at the hole contactin silicon heterojunction (SHJ) solar cells, leading to a reduction of parasitic absorption and a JSC improvement on average of 0.5 mA/cm 2 .• Influence of MoOx thickness and annealing condition on the SHJ cell performance was studied and optimal parameters were determined.• Impact of MoOx thickness and anneal treatment on the thin film interfaces at the hole contact was investigated and an interfacial dipole in the form of a-SiOx was postulated.• A glass to glass 1-cell mini-module was fabricated using a MoOx-contacted SHJ cell.• After damp-heat testing, good long-term stability was achieved at module-level, with a degradation of less than 3%abs (passing the IEC61215 standard).
Recent research has shown that bifacial PV modules with a glass/glass packaging are prone to different PID mechanisms occurring simultaneously on the front and the rear side of the solar cell. With this in mind, researchers investigating the impact of PID on each side of the bifacial solar cell separately apply PID stress to one side of bifacial PV modules according to stress method (b) as described in the IEC TS 62804‐1, that is, contacting the surface with a conductive electrode. Yet, in this paper, we show that such practice of PID testing might result in an unintended development of an electric field between the environmental chamber and the nonstressed side of the solar cell. Through our experimental study, we reveal that this electric field results in unintended bifacial PID stress of bifacial solar cells, which goes along with misleading interpretations of the evolving PID mechanisms and susceptibility of bifacial PV modules. Next to the methodology concerns, we discuss three possible solutions to prevent such unintended PID mechanisms from occurring.
Since massive numbers of photovoltaic (PV) modules are expected to be discarded in the next decades, it is important to think about end-of-life management for those PV modules and to include re-use next to recycling. However, the reuse of decommissioned PV modules is a quite complex subject since there are requirements from technical, economic, environmental and legislative point of view. An evaluation of possible applications for second-hand PV modules showed that currently, the use of these PV modules in high-income countries is only interesting for specific applications. These are the replacement of some defect modules to repair PV systems (that usually still receive feed-in tariff) or the replacement of all PV modules for either a low-cost extension of system lifetime or the repowering of severely underperforming systems. For low-income countries, second-hand PV modules are interesting to build new small to medium size PV systems (often off-grid). The typical decommissioned PV module is a crystalline silicon glass-backsheet module from a utility power plant. Most PV modules originate from plants that have been partly damaged by severe weather or from repowered plants that did not receive feed-in tariff (anymore). Currently, technical requirements to qualify potentially re-usable PV modules for re-use are lacking. In the legislation also, a clear criterion for a PV module to be considered functional is needed, since it is not an easy yes/no situation like for a typical electronic device. In this paper, guidelines for a low-cost quality inspection and costeffective PV module repair are given. It is proposed to set a clear performance threshold at 70% of the original power for a PV module to be not considered as waste. With this paper, we aim to open the dialogue on a commonly accepted re-certification protocol and threshold values. Currently, the worldwide re-use market size is estimated to be around 1 GWp/year, of which 0.3 GWp/year is originating from Europe (mainly Germany, with Italy rapidly coming up). Many second-hand PV modules are shipped to developing countries without recycling facilities which might create the risk of disposal on the longer term. To create a healthy and sustainable market for second-hand PV modules, it will be important that evaluation standards for potentially re-usable PV modules become available
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