EnabledFuture: Metal Recovery in Photovoltaic Modules
Anaïs Engelmann, Researcher, Enabled Future Limited
1. The Market for Solar PV Technology
Solar power is playing a major role in the global renewable energy transition with new capacity installations accounting for more than all other renewable technologies in 2021 combined. (Solar Power Europe, 2022) However, the success of solar comes with a dark side – the deployment of solar photovoltaic (PV) modules is forecasted to result in 78 million tonnes of module waste in landfill by 2050. (IRENA, 2016) Immediate action is required to prepare for this incoming waste stream and to divert it from contributing to the electronic waste crisis.
2. Drivers and Challenges for Tackling Solar PV Waste
Currently, only 10% of PV modules are reused and/or recycled worldwide with the rest ending up in landfill, creating significant environmental issues given the presence of hazardous metals including lead and tin, and the depletion of virgin materials. (Koch, 2015) This can be primarily attributed to a lack of economic incentives, due to the low value of the currently recovered material components, coupled with the high recycling costs of their separation and processing. This section examines the current drivers and challenges to implementing circularity within the end-of-life (EoL) solar PV supply chain.
2.1 Recovery Economics
A major barrier to higher PV recycling rates is the lack of profitability, which is demonstrated in the case of crystalline polysilicon (c-Si) modules, making up 95% of the PV technology market share. (IEA, 2022) With the recovered value of secondary materials taken into account, it currently costs around $20-30 to recycle a single c-Si panel, versus the $1-2 of sending it to landfill. (Wesoff & Betz, 2020) Other estimates put the relative costs of recycling and landfill in the USA at $15-45 per panel and $1-5 per panel respectively. (Deng, Chang, & Green, 2021)
However, the current value extracted from commercial PV recycling methods focuses on glass and aluminium components and does not fully exploit the potential value recovered from the present metals such as silver, copper, and silicon. There is an opportunity here for emerging PV chemical recycling technologies to focus their efforts on obtaining these lower content, yet higher value materials, which could result in lower net recycling costs or even a profit. However, there are several challenges currently faced in the recovery of such metals which are preventing their full value from being extracted.
In the case of silver, the relatively small amount found in EoL modules means its recovery is only economically feasible in large single-lot quantities of around 30-40 tonnes, due to freight expenses. Therefore, due to current waste stream volumes, the financial benefits are insufficient to justify silver-specific recovery schemes. R&D efforts are ongoing to increase silver recovery yields to improve the business case for its recovery.
In addition, for recovery to be scalable, a grading system must be put in place to classify types of PV waste and their associated silver values. However, silver content varies greatly between different panel types, particularly within amorphous crystal panels, ranging between 4 and 10 grams per panel in quantity. This creates issues in terms of standardisation, creating a further barrier to scalability. (Marchisio, 2022)
A well organised recycling facility with appropriate analytical and diagnostic capabilities should also be able to categorise and stream solar panel waste and this approach is normal in other types of recycling e.g., catalysts and batteries. However, it will be some time before such state-of-the-art facilities become commonplace.
In the case of metallic silicon, research shows potential for its waste stream to be made fully circular, but challenges are faced in terms of its purity when recovered. Silicon must be fully purified to be reinserted back into the PV supply chain, requiring high energy and complex understanding of impurities left in the recycled silicon. (Hutchins, 2022) As a result, the relative value of silicon metal is currently too low to be economically feasible, leading to a lack of silicon recovery supply chains and infrastructure.
2.2 Collection Systems and Frameworks
Key activities in creating a scalable, circular PV supply chain are the decommissioning, collection, and transportation of modules from the owner to recycling facilities, relying on participation from several stakeholders. Implementation of collection into supply chains enables this activity, with existing services typically falling under one of two categories. The first is the original equipment manufacturer (OEM) take-back schemes, where the module manufacturer has an established internal recycling infrastructure. For instance, US-based module manufacturer First Solar offers a recycling service agreement for an added fee, wherein the customer can drop off an EoL module at a region-designated collection point. (First Solar, 2022)
The second service model is where collection systems are provided by a third-party recycler, who engages with the EoL module on behalf of OEMs. (H. Salim, 2019) For instance, PV Cycle offers their Distributor Take-back Scheme in the UK, where quantities of under 20 modules can be taken to dedicated collection facilities free of charge. (PV Cycle, 2022) However, in cases where services rely on owner responsibility to uninstall and transport modules to their nearest facility, customer motivation and a lack of incentive can be barriers. Collection of EoL electronic products has proved to be significantly more effective in countries where legislation ensures that responsibility falls on the OEMs as opposed to the product owner. (OECD, 2022)
At present, only the EU has implemented a fully legislative approach, by incorporating solar waste into the Waste Electrical and Electronic Equipment Directive (WEEE) (2012/19/EU) as of 2012. This directive obligates manufacturers to collect at least 85% of their PV modules. Each EU member state has been required to transform this legislation into national law and define the rules behind collection and recycling, falling into two financial model categories. Firstly, producer-financed compliance cost models, where the producer finances EoL management through joining a compliance scheme and either paying a recycler directly or joining a stewardship programme. Secondly, consumer-financed upfront recycling fee models, where the consumer pays an additional fee at the time of module purchase, to go towards either offsetting current recycling costs or to set aside as an estimate for future recycling costs. (IRENA, 2016) These different models have been summarised in Figure 1.
Countries outside of the EU’s mandatory framework operate under a voluntary framework, where producers either take a direct management approach and implement their own recycling infrastructures and services, or an indirect management approach. Under indirect management, the producer’s involvement can range from contracting service providers to handle waste management, to leaving the responsibility completely up to the consumer, which inevitably results in higher landfill rates. (IRENA, 2016)
2.3 Recycling Infrastructure
Alongside having collection systems in place, recycling infrastructure is another fundamental component for supporting the transition to a circular PV system. Module designs and the difficulty in material separation mean that distinct industrial processes are needed to recycle them. (Vekony, 2021) This creates the challenge of providing the necessary infrastructure to accommodate such process, and on a large enough scale to meet demands. Pilot projects of varying scale have been rolled out both privately and by research initiatives; a 2015 review of recycling infrastructure found that eight laboratory processes, two industrial pilot plants, one industrial plant and one patent had been developed thus far, with only three of those reaching an industrial level. (CucchiellaIa, D’Adamo, & Rosa, 2015)
Progress has been made within this space. For instance, the PV Producer Responsibility Organisation Soren (previously PV Cycle France, an organisation dedicated to the circularity of solar modules) has been working on several industrial-scale projects. It operates by calling for tenders and commissioning partner recycling companies. Soren partnered with the French utilities company Veolia in 2017 to open an industrial scale solar panel recycling site in Rousset, France with a capacity of 4,000 tons of PV waste annually. In September of 2022, another recycling plant was inaugurated by Soren in Saint-Loubès, France in partnership with Envie 2E Aquitaine, a French company offering WEEE collection and management services for authorities and professionals. Again, this has a capacity of 4,000 tonnes of PV waste annually and reports 95% recycling rates. This progress demonstrates the identified value potential within waste-focused industries.
3. Value Potential in Metal Recovery
Two EoL scenarios – early-loss and regular-loss – from a recent IRENA study are presented to examine value potentials whilst accounting for different uncertainties. Under the regular-loss scenario, a 30-year solar panel lifespan is assumed with no early attrition, projecting 1.7 million tons of PV waste by 2030 and 60 million tons by 2050. Under the early-loss scenario, infant and midlife failures are considered, projecting 8 million tons of PV waste by 2030 and 78 million tons by 2050 respectively. These two scenarios would amount to a cumulative $248 million and $1.1 billion of recoverable crystalline silicon value respectively becoming available for recycling. (IRENA, 2016)
Today, materials such as silicon, silver, and copper are not separated out in recycling methods, but rather just shredded and sold with the recovered glass. (Calma, 2022) The implementation of the aforementioned legislative and infrastructural drivers, coupled with continuous R&D in efforts in these areas, could unlock a huge amount of recovered material value from PV waste, considering silicon, silver, and copper account for two-thirds of the monetary material value. (Peplow, 2022) Given the material composition of a c-Si module as shown in Table 1, estimates can be made for the total recoverable value potential of the metal contents with regards to future waste streams. An average weight of 22kg per module has been used in calculations. (Latunussa, Mancini, Blengini, Ardente, & Pennington, 2016)
In the case of crystalline silicon, metallurgical-grade silicon with 99% purity has a value of approximately $4 per kg. (Peplow, 2022) Assuming the 99% purity can be achieved, that would amount to around $3.12 of recovered secondary silicon sold per module, and $146 per ton of PV waste processed. However, for silicon to be reinserted into PV production supply chains, solar-grade silicon with a minimum of 6N grade purity is required. If such purity in secondary silicon is attained, the total recoverable value could soar to around $30 per kg, meaning $1,095 per ton of PV waste processed. Under IRENA’s regular-loss and early-loss scenarios, this would equate to $1.86 billion (1.7 million tons of PV waste) and $8.76 billion (8 million tons of PV waste) respectively by 2030. (IRENA, 2016) Such high purity is yet to be achieved, but several R&D projects are already in motion to work towards unlocking this full value through soft chemistry mechanisms. These are described in the following section.
In the case of silver, assuming a conservative 4 grams recovered per solar module and a current market value of $0.66 per gram (Bullion By Post, 2022), there is a total potential value of up to $2.64 per module in resale value. Under IRENA’s regular-loss and early-loss scenarios, this would equate to $594 million (1.7 million tons of PV waste) and $2.8 billion (8 million tons of PV waste) respectively by 2030. Current silver recovery yields are around 95%, and so with continued R&D these values could be further maximised. (Latunussa, Mancini, Blengini, Ardente, & Pennington, 2016)
In the case of copper, the material is found in both the copper wires connecting the cells (soldered on with tin and lead), and the internal conductor material. Assuming a full recovery of 0.47kg of copper per module and a scrap market resale value of $3.49 per kilogram (H&S Metals, 2022), there is a total potential value of $1.65 per module. Under IRENA’s regular-loss and early-loss scenarios, that would equate to approximately $127 million (1.7 million tons of PV waste) and $597 million (8 million tons of PV waste) respectively by 2030.
In the case of aluminium, the material is predominantly found in the frame, as well as the internal conductors within the solar cells. Assuming a full recovery of 4.08kg of aluminium per module and a scrap resale value of $0.51 per kilogram (H&S Metals, 2022), there is a resale value of $2.08 per module, equating to regular and early loss scenarios of $160.7 million (1.7 million tons of PV waste) and $756.4 million (8 million tons of PV waste respectively by 2030.
In total, this would amount to between 0.4 and 1.9 million tons of solid PV waste recycled worth based on today’s metal prices between $1 and $2.2 billion in value recovered.
Table 2. Regular and Early Loss Scenarios for PV Module Material Value Recovery
While the metal recovery revenues are attractive, when solar panel recycling is mandated by legislation, or where OEMs choose to take responsibility for EoL panel disposal for ESG compliance, certified recyclers can charge panel OEMs treatment and processing charges which alone make it a valuable business for them. Material recovery values are more important when there are voluntary systems for PV module recycling.
4 Recovery Methods
To capture the identified value potential in metal recovery, improved recycling methods are required to increase metal yields and to decrease processing costs. Though still in their early stages across the industry, there are now several companies with emerging technologies and research working towards improving these factors.
The Full Recovery End-of-Life Photovoltaic (FRELP) process is an EU-funded project that ran between 2013 and 2016 with a €4.7 million budget. (FRELP, 2022) The project was coordinated by Sasil S.p.A, Stazione Sperimentale del Vetro, and PV Cycle, with the objective of achieving 100% recyclability rates. This is considered one of the most advanced methodologies for material recovery in c-Si PV waste panels, with precious metal recovery rates of 74.5% (copper), 38.6% (metallic silicon) and 11.3% (silver). (Markert, Celik, & Apul, 2020) Though the initial objectives were not fully achieved, partial results were achieved in the form of a pre-prototype. (European Commission, 2021)
The FRELP process has the following steps: the PV frames, cables and glass are removed, leaving behind the remaining layers of polymers and cells which are treated in an incineration plant. The obtained ashes are sieved and treated by acid leaching with nitric acid, then filtered to recover the metallic silicon which is further treated with electrolysis to recover the silver (using graphite rods) and copper. (Ardente, Latunussa, & Blengini, 2019) Following the EU’s most recent technical report of the FRELP method in 2015, it was found that for 1 ton of PV waste, 36.5kg of silicon metal could be recovered by filtration after leaching and resold in the metallurgical sector, and 1.67kg of copper and silver could be recovered at cathodes following electrolysis also for market resale. (FRELP, 2022)
Other efforts to improve current metal recovery rates and costs are emerging from different private companies. The recycling start-up TG Companies, based in Tucson, Arizona in the US, has developed a patent-pending chemical process used to extract silver, tin, copper, and lead from PV cells, leaving behind just the metallic silicon. Their method includes heat treatment to boil off the EVA protective layer, using temperatures below 500°C to operate the oven and avoiding the leaching of iron and copper into the solar cell. The company predicts the recovery of $15 worth of silver per module by achieving 95% recovery at 99.9% purity. They aim to have their first pilot plant running by 2024 with a recycling target of 100,000 PV modules annually. (Hanley, 2022) (Ferrell, 2022)
ROSI Solar, headquartered in Grenoble, France, is a company offering innovative solutions for recycling and revalorization of raw materials in the PV industry. Its CEO is physicist and entrepreneur – Yun Luo and co-founder is silicon product expert – Daniel Bajolet, former VP of Rhodia. Its Chief Technology Officer (CTO) is Guy Chichignoud. ROSI’s technologies enable recovery of ultra-pure silicon and other metals currently lost during the production of photovoltaic cells and at the end-of-life (EoL) of solar panels. (ROSI Solar, 2022) They belong to the consortium ICARUS and are financially supported by the EU’s Horizon programme.
ROSI Solar is developing technology to improve the efficiency and costs of material separation, allowing them to recover ultra-pure silicon as well silver fingers from a cell, using a combination of physical, thermal, and soft chemistry mechanisms.
In solar panel production, waste is created when silicon ingot raw material is sawed using a diamond wire into wafers (less than 200 µm thick). Some 40% of the material is lost into a sludge (“kerf”) created as micro-chips of silicon mix with the sawing liquid and historically this has been disposed of rather than recovered. An estimated 200,000 tons of silicon worth $1.5 bn is lost in this way and the amounts will increase as solar panel production rates increase. ROSI’s kerf recovery technology helps manufacturers to save on kerf disposal costs and creates value by separating out the silicon from the sawing liquid. The silicon particles can be washed and used to make ultra-pure silicon granules for fresh silicon ingot and the liquid can be reused in the sawing process. (ROSI Solar, n.d.)
A patent family (WO2020007720A1) assigned to CNRS with ROSI’s CTO as one of the inventors describes a treatment process involving high temperature melting and granulation of the kerf. Silicon melts at 1,410 °C and the process requires temperatures of ~1450°C to obtain molten silicon. A first pre-granulation step using a crucible and capillary to form a discontinuous flow of molten silicon droplets which are atomised to form solid metal granules by fragmenting and solidifying the droplets received on a cooled rotating disc to form solid metal granules. (Chichignoud & Faveau, 2020)
ROSI Solar differentiate themselves from silicon recyclers by offering higher purity silicon, achieving up to 5N (99.999%) purity. 5N grade silicon both exceeds the 3N purity requirement for metallurgical-grade silicon and provides the environmental advantage of requiring less energy in the purifying process for higher grade application such as battery semiconductors (5-6N) and reuse in the PV supply chain (9-11N).
Furthermore, there is a current gap in the market for local European suppliers, with most high-grade silicon being imported from Asia. ROSI intends to fill this gap through PV metal recovery, particularly given market trends towards an increase in silicon demand, such as batteries which are starting to see silicon incorporated into anode technologies. Though still in their pilot phase, ROSI Solar will launch their first industrial site in 2024 in collaboration with French solar panel producer responsibility organisation Soren and Saint-Loubès based waste service provider Envie 2E Aquitaine. The facility has an expected treatment capacity of 3,000 panels per year, eventually increasing to 10,000 per year. ROSI also has ambitions to expand sites to Germany and eventually other European countries. Battery and semiconductor manufacturers are predicted to be the main secondary market customers, and a key activity soon will be working with those customers to identify what state of recycled silicon best meets their needs.
It has also been suggested that diverting silicon to applications with lower purity requirements is the best option for maximising recovery, as recovery costs for lower purity would be significantly cheaper. For instance, a team of scientists from the Agency for Science, Technology and Research (A*STAR) and Nanyang Technological University, Singapore (NTU Singapore) has proposed using such silicon for high-performance thermoelectric devices that convert heat into electricity, as thermoelectric devices which are tolerant to defects and impurities, making them suitable for recycled silicon. Their proposed technique would include pulverising polycrystalline silicon into powder and pelletising it into ingots, using spark plasma sintering to dope the silicon with germanium and phosphorus. (Bellini, 2022)
Similarly, Korean company MGInnovation Ltd. filed a patent in 2021 for the use of silicon recovered from polycrystalline silicon wafers, as a raw material for anode material additives for lithium ion batteries (LIBs). This invention uses silicon sludge recovered during the manufacturing process (as opposed to EoL silicon), and this sludge contains 30% or more of ultra-high purity silicon nanoparticles. (Korea Brevet n° KR20210152604A, 2021) Using silicon derived from the sludge in battery anodes provides several benefits over silicon powder, such as higher purity, higher reactivity, and ease of chemical bonding due to the energy generated during silicon wafer manufacturing. This shows great potential for redirecting silicon from PV waste streams into different applications.
While there is much promising activity as described in this article, many of the solutions are still in a relatively early stage development. Companies with existing pyrometallurgical scrap material who can specialise in large volume/low grade scrap recovery hold the most promise with handling future PV waste streams, given their pre-existing market expertise and infrastructure. To facilitate this, manufacturers have also started working with recyclers to improve the module designs for disassembly. For instance, Solarge is a Dutch PV manufacturing company whose modules are designed for improved extraction of materials, having already achieved better extraction results for silicon and silver compared to conventional PV modules. This can be attributed to easier material separation, no cross contamination or dangerous by-products, and less energy required for separation, also leading to lower costs and improved scalability. Their initial production capacity will be 100 MW/year, with ambitions to scale up beyond 350 MW/year. (Gerven, 2022)
A summary of the key companies with promise for future scale-up of solar PV recycling is summarised in Table 3.
5 The Future for PV Recycling
Forecasted PV waste streams will significantly add to the global electronic waste production crisis unless PV recycling at scale is achieved within the next 10 years. Future implementation of regulatory approaches and infrastructure will be key enablers to avoiding large PV landfilling volumes, however complete reliance on this is insufficient. Recycling economics must also be improved to reduce processing costs and increase recoverable value.
Capturing the value of the metals present in PV modules provides a great opportunity, both for driving business within secondary raw material waste streams and diverting panels away from landfill. If higher recovery rates can be achieved through R&D for materials such as silicon metal, copper and silver, processing costs can be significantly decreased. This will be further enabled by scales of economy as PV waste streams increase over the coming years.
This can be accelerated by improved regulatory measures globally regarding extended producer responsibility for PV waste. Mandating manufacturers to handle their EoL modules would incentivise R&D for higher value recovery as well as improved collection infrastructures.
About The Author
Anaïs Engelmann is a recent graduate of Design Engineering at Imperial College London, now working at Enabled Future Limited researching solar panel recycling technologies. This work is a continuation of her Masters’ project, where she developed a web tool to facilitate recycling decisions for solar panel supply chain stakeholders. Alongside her work at EFL, she is working on the startup Team Repair, which she co-founded during her time at university. Team Repair is a circular business aimed at engaging children with STEM subjects through teaching them how to repair electronics.
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