Large-scale deployment of photovoltaic (PV) modules has considerably increased in recent decades. Given an estimated lifetime of 30 years, the challenge of how to handle large volumes of end-of-life PV modules is starting to emerge. In this Perspective, we assess the global status of practice and knowledge for end-of-life management for crystalline silicon PV modules. We focus in particular on module recycling, a key aspect in the circular economy of photovoltaic panels. We recommend research and development to reduce recycling costs and environmental impacts compared to disposal while maximizing material recovery. We suggest that the recovery of high-value silicon is more advantageous than the recovery of intact silicon wafers. This approach requires the identification of contaminants and the design of purification processes for recovered silicon. The environmental and economic impacts of recycling practices should be explored with techno–economic analyses and life-cycle assessments to optimize solutions and minimize trade-offs. As photovoltaic technology advances rapidly, it is important for the recycling industry to plan adaptable recycling infrastructure. The increasing deployment of photovoltaic modules poses the challenge of waste management. Heath et al. review the status of end-of of-life management of silicon solar modules and recommend research and development priorities to facilitate material recovery and recycling of solar modules.

Research and development priorities for silicon photovoltaic module recycling to support a circular economy

This article examines some of the basic questions about silicon module recycling: (1) What can be recovered from silicon modules? (2) What recycling technologies are needed? (3) What are the potential revenues for different recycling scenarios? And (4) what are the major challenges for different recycling scenarios? Three recycling scenarios are considered: module reuse, component extraction, and material extraction. Recycling process sequences for different scenarios are outlined. The discussions conclude that module reuse generates the highest revenue with the fewest processing steps, while material extraction leads to the lowest revenue with the most processing steps. It is suggested that gentle and clean separation of silicon solar cells from the glass pane is a critical technology for silicon module recycling. It is also argued that two low-concentration metals must be recovered from silicon modules: silver as a scarce material and lead as a toxic material. Their recovery requires chemical methods, while bulky materials including glass cullet, aluminum frame, and copper wiring can be recovered with physical methods. The silicon in the cells can be extracted with different qualities: ferro-silicon, metallurgical-grade silicon, or solar-grade silicon, with a higher revenue and more complicated recycling process for purer silicon. Markets outside the solar industry for the recovered silicon should be explored. The biggest challenge for module reuse is to find a large and sustained market for hundreds of gigawatts peak of decommissioned modules a year, and the biggest challenge for component extraction is the many different module and cell structures on the market and cell efficiency variability. For all the three scenarios, the cost of collecting and processing waste modules is a common challenge.

Major challenges and opportunities in silicon solar module recycling

The rapid development of photovoltaic (PV) industry has led to increasing emissions of silicon-based solid (SIBS) waste. The discharge of these solid wastes is not only detrimental to the recovery of valuable resources, but also poses a certain threat to the environment. Although some decentralized studies had been conducted on these wastes, either metallurgical silicon slag, waste crucibles, silicon cutting wastes, or EOL photovoltaic panels, few studies had systematically analyzed the comprehensive utilization of SIBS waste from the perspective of whole PV industry. This work firstly reviews the comprehensive utilization status of SIBS waste, and then analyzes the silicon metal value chain related to PV industry. Finally, it concludes the development advantages, risks and challenges in PV industry, and puts forward a few suggestions on closed and/or opened loop recycling of SIBS waste in PV industry chain. From the perspective of entire industrial chain, systematically sorting out the comprehensive utilization of SIBS waste will provide a theoretical reference for the green and sustainable development of PV industry.

An overview of the comprehensive utilization of silicon-based solid waste related to PV industry

The photovoltaic industry has shown vigorous growth over the last decade and will continue on its trajectory to reach terawatt-level deployment by 2022–2023 and an estimated 4.5 TW by 2050. Presently, its elaboration is driven primarily by cost reduction. Growth will, however, be fuelled by the consumption of various resources, bringing with it unavoidable losses and environmental, economic, and societal impacts. Additionally, strong deployment growth will be trailed by waste growth, which needs to be managed, to support Sustainable Development and Circular Economy (CE). A rigorous approach to quantifying the resource efficiency, circularity and sustainability of complex PV life cycles, and exploring opportunities for partially sustaining industry growth through the recovery of high-quality secondary resources is needed. We create a high-detail digital twin of a Silicon PV life cycle using process simulation. The scalable, predictive simulation model accounts for the system's non-linearities by incorporating the physical and thermochemical principles that govern processes down to the unit operation level. Neural network-based surrogate functions are subsequently used to analyse the system's response to variations in end-of-life and kerf recycling in terms of primary resource and power consumption, PV power generation capacity, and CO2 emission. Applying the second law of thermodynamics, opportunities for improving the sustainability of unit operations, the larger processes they are the building blocks of, and the system as a whole are pinpointed, and the technical limits of circularity highlighted. We show the significant effects changes in technology can have on the conclusions drawn from such analyses.

The resources, exergetic and environmental footprint of the silicon photovoltaic circular economy: Assessment and opportunities

Glass is a material inextricably linked with human civilization. It is also the product of an energy intensive industry. About 75%–85% of the total energy requirements to produce glass occur when the raw materials are heated in a furnace to more than 1500 °C. During this process, large volumes of emissions arise. The container and flat glass industries, which combined account for 80% of total glass production, emit over 60 million tonne of CO2 per year. However, environmental issues relating to the glass industry are not just limited to the manufacturing stage, but also from raw materials extraction, which impacts local ecosystems and creates other environmental challenges associated with tailing ponds, waste disposal and landfills. This systematic review poses five questions to examine these issues and themes: What alternatives exist to abate the climate effects of glass and thus make the full life cycle of glass more sustainable? What are the key determinants of energy and carbon from glass? What technical innovations have been identified to make glass manufacturing low to zero carbon? What benefits will amass from more carbon-friendly process in glass manufacturing, and what barriers will need tackling? To examine these questions, this study presents the findings of a comprehensive and critical systematic review of 701 studies (and a shorter sample of 375 studies examined in depth). A sociotechnical lens is used to assess glass manufacturing and use across multiple sectors (including buildings, automotive manufacturing, construction, electronics, and renewable energy), and options to decarbonize. The study identifies a number of barriers ranging from financial to infrastructural capacity, along with high potential avenues for future research. 

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Elisabeth Lemaire

Papers

Towards a circular supply chain for PV modules: Review of today's challenges in PV recycling, refurbishment and re-certification