ReviewRecent progress in silicon photovoltaic module recycling processes
Graphical abstract
Introduction
Solar photovoltaics (PV) are one of few renewable, low-carbon energy sources with both scalability and affordability (Jean et al., 2015; Taylor et al., 2020), which will gradually replace fossil fuels to meet growing global energy demands in a decarbonised society (Taylor et al., 2020). By the end of 2020, the global PV installation capacity exceeded 750 GW, and it is expected to reach 1 TW by 2023 (ITRPV, 2021). Solar panels have an average 25-year lifetime. As installation capacity grows, the volume of end-of-life (EoL) modules will also grow and reach a million-ton scale by 2030, with more than 80% being crystalline silicon photovoltaic modules (IRENA and IEA-PVPS, 2016). If these materials can be recycled properly, two billion new modules (equivalent to a 630-GW capacity) can be manufactured using the recycled materials (IRENA and IEA-PVPS, 2016). The circular economy approach preserves energy, materials, and value (Thomassen et al., 2022).
Waste PV modules are a reservoir of valuable materials, including aluminium, copper, silver, silicon, and glass. There are four main benefits of recycling panels at the end-of-life: mitigating material depletion (e.g., silver), avoiding toxicity emissions into the environment (e.g., lead and fluorine), creating economic revenue by recovering valuable materials from the panel (e.g., aluminium, copper, and high-purity silicon and silver), and avoiding the energy investment to produce virgin materials to replace them (Seo et al., 2021).
Various recycling processes have been developed to recover these raw materials from modules, exhibiting different processing efficiencies, recycling yields, costs, and environmental impacts. However, commercial-scale PV recycling hardly exists.
There are several review papers in this field, looking at different perspectives, time scales and different country contexts. The first technology review was published in 2015, by Tao and Yu (2015). This study reviews early-stage developments in recycling PV manufacturing waste and end-of-life modules. Padoan et al., 2019 extended the scope of the review to cover both patented and published recycling processes for PV modules by 2018(Padoan et al., 2019). Chowdhury's work discussed several promising recycling approaches in the context of the regulatory framework and political status, which scrutinized the necessity of PV recycling policy in PV end-of-life management (Chowdhury et al., 2020). Guo et al.’s work focused on silicon recycling from both manufacturing waste and end-of-life modules (Guo et al., 2021). Deng et al.’s work analysed the economic feasibility of mainstream recycling processes and concluded that high-value recycling processes are more expensive but have significant potential for processing improvement to achieve higher potential revenue (Deng et al., 2019). Lunardi et al. conducted comparative life cycle assessments for three recycling processes with published process details and concluded that all the analysed recycling scenarios can reduce environmental impacts effectively in human health, ecosystem and resources categories compared to landfill and incineration scenarios (Lunardi et al., 2018). This work also highlights the emissions during waste PV module transportation. The latter three policy, economic and environmental assessments took primary data from earlier publications with sufficient processing details (Latunussa et al., 2016a) because other processing data were unavailable. Overall, recent progress in innovative recycling processes provided new insights and new processing data to improve the current understanding of technical feasibility, economic viability, and social desirability.
It is important to summarise the limitations and possible improvements for emerging new processes. This paper aims to provide a comprehensive overview of the progress in silicon PV module recycling processes, at both the lab scale and pilot scale over the last decade, focusing on the mechanism, recycling yield, advantages and disadvantages, and areas for improvements for different recycling processes. We highlight the recent progress from 2018 to 2021 in full recovery to complement existing knowledge.(Chowdhury et al., 2020; Deng et al., 2019; Farrell et al., 2020; Lunardi et al., 2018b; Tao et al., 2020) Some existing channels and potential markets are also identified for recycled materials, both within the PV industry and outside of the PV industry. Even though most of the research was conducted in laboratories, critical new insights can be drawn to guide the development of scalable, affordable, and sustainable PV recycling technology to manage the upcoming waste surge. Feasibility, viability, and desirability matrices are proposed to assess the commercial potential of a new recycling process.
Databases such as Google Scholar, Web of Science, and ScienceDirect were primarily used to obtain literature. Industry reports and conference proceedings were also acquired to assess the latest processes. The purpose of this review is to draw similarities and differences among hundreds of PV recycling processes to be able to identify the trends and gaps during process development. We selected 67 published experimental papers and 79 granted patents between 2011 and 2021 as the main objects of this study, which covered the most recently reported outcomes in the field of end-of-life PV recycling, focusing on the specific material recycling and process optimisation in the aspects of academic and application.
Section snippets
Photovoltaic modules
The structure of a silicon photovoltaic module can be compared to a “sandwich,” with a thin layer of valuable materials encapsulated within glass sheets and framed with aluminium, as shown in Fig. 1. The thin layer is composed of solar cells and interconnecting ribbons, which account for approximately 5% of the weight but more than half of the value (Table 1). The substrate of a solar cell is a high-purity (usually exceeding 99.9999% purity) silicon wafer (4.4%w). Silver (0.03%w) and aluminium
Recycling processes for silicon photovoltaic modules
Mass recovery refers to a process that crushes PV sandwiches and reuses the contaminated materials in low-value applications (Held, 2013; Wambach, 2017). Modules are downcycled primarily because the process is not customised to treat solar panels. (Sustainability Victoria, 2019). For example, one study demonstrated that crushed fine glass particles (0–2 mm) can be reused to replace up to 30% of the conventional fine aggregate (natural sand) used in manufacturing mortar (Audoin et al., 2017).
Secondary markets for recycled products
So far, investigations of silicon PV module recycling mostly focus on recycling processes. Identifying a suitable market to integrate recycled materials ultimately enables circular business models. Aluminium frames and recycled silver have a large and sustainable market demand. They are openly traded in the recycled material market with different pricing matching different purity levels, e.g. 925 silver (92.5% purity) and 999 silver (99.9% purity). However, it is more challenging to find a
Trends in the past decade
Top PV installation countries and regions, including the US, the EU, China, Australia, Korea, Japan, and India, have conducted extensive studies on this topic, including stakeholder surveys (Mathur et al., 2020; Salim et al., 2019a, 2019b; Tsanakas et al., 2019; Wakefield-rann et al., 2020), lab-scale process development (Chung et al., 2021; Draoua et al., 2017; Pagnanelli et al., 2019; Rubino et al., 2020; Syvertsen et al., 2017), life cycle assessment (Ardente et al., 2019; Bartie et al., 2021
Technical
Technical challenges exist for large-scale solar panel recycling. These barriers demotivate recycling initiatives and favour simple landfill, stockpiling, or downcycling. The intrinsic barrier is the low value (Tao and Yu, 2015; Tao et al., 2020) and low quality (Farrell et al., 2020; Heath et al., 2020) of recycled materials from currently industrial-scale recycling plants. Recycled materials are usually contaminated, which makes them only suitable for downcycling rather than recycling. The
Conclusion
Solar panel recycling is in its infancy with both technical and non-technical challenges. This paper provides a comprehensive overview of technology progress in silicon photovoltaic module recycling to guide future research and development. Technology solutions exist, but they need further improvements in recycling yields, costs, and social impacts for large-scale practices.
Recycling can be divided into four steps: disassembly, delamination, material sorting, and material extraction. The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The financial support from the Australian Renewable Energy Agency (2020/RND015), Australian Research Council (DP220100306), and Australian Centre for Advanced Photovoltaics (ACAP) is acknowledged.
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These authors contribute equally to this work.