Photovoltaic (PV) Panel Waste Volumes

Summary

Beyond general waste regulations, various approaches have been developed specifically to manage end-of-life PV panel waste. This series examines value creation from photovoltaic panels that have completed their service life. At each stage of the value chain, particularly at the end of the lifecycle, there are opportunities to create value from PV panel waste. This article addresses opportunities related to reducing material use, repair and reuse options, and considerations regarding recycling and processing of PV panel waste.

Reduce, Reuse and Recycle Options for Photovoltaic Panels

The fundamental principles of the circular economy (cradle-to-cradle opportunities) and the 3R waste management principles (reduce, reuse, recycle) can be applied to solar panels (see Waste Management Options section). Among these options, the priority is reducing material use in solar panels and correspondingly increasing efficiency. Strong market growth, raw material scarcity, and downward pressure on solar panel prices drive more efficient mass production, reduced material use, material substitution, and the promotion of higher-efficiency new technologies. This contributes to efforts to reduce material consumption per production unit. The reuse option comes after the reduction option. This includes various repair and reuse methods. Recycling is the least preferred disposal option and is applied only when the first two options are exhausted. This is used for processing and treating solar panels and can help obtain raw materials for new solar panel production or other products (see Figure 1).

PV Panel Material Savings Through R&D (Reduction)

The following analysis will summarize potential "reduction" options for material components used in different PV technologies.

Resource and Material Efficiency Definitions

Resource and material efficiency means the effective use of resources and materials required to successfully complete a product or process. This includes optimal use of energy, water, raw materials and other resources and minimization of waste. It also includes sustainable practices such as waste reduction, promotion of recycling, and use of reusable materials. Resource or material efficiency aims to minimize environmental impact by using limited resources sustainably. This approach enables creating more value with fewer resource or material inputs. The material mix used in PV panels has not changed significantly in the past, but material savings have been achieved through increased resource and material efficiency. For example, the quantities of hazardous materials such as lead, cadmium, and selenium have been reduced and substitution work has been undertaken. In other PV panel technologies, material quantities are being minimized to reduce costs. While consumption of rare and valuable materials will increase with PV market growth, there is currently no major concern regarding availability and prices. However, it is understood that in the long term, critical materials may cause limitations. Additionally, rising prices will encourage recycling activities and support investments in more efficient mining processes. In summary, research on material use and sustainability of PV panels continues. PV R&D has identified priority topics on reducing or replacing material use for different components commonly used in current PV panels 16. Examples in this context include: • c-Si panels: glass, polymer, silicon, aluminum, silver and lead; • CIGS panels: glass, polymer, aluminum, cadmium, gallium, indium, selenium; • CdTe panels: glass, polymer, cadmium telluride, nickel. Furthermore, significant R&D efforts have been concentrated on new materials and material modifications. New transparent conductive oxide layers using more common and thus cheaper compounds such as indium fluorine tin oxide could reduce the use of indium tin oxide as a front electrode. This reduces indium use in indium tin oxide used in thin-film solar cells.

Glass

Further optimization of glass composition, thickness, anti-reflective coating, and surface structure could increase front glass panel transmission by 2% by 2024. The use of two millimeters or thinner glass with single-glass lamination would require additional mechanical balancing efforts, and this could be investigated with double-glass panels used in thin-film solar panels for years through an encapsulation layer. This could lead to significant material savings by eliminating the need for a back layer.

Polymers

Today, quaternary materials dominating the market are not recyclable because they cannot be dissolved or degraded, so encapsulants and back-sheet films are not recycled. Research is working on reducing or replacing the amount of polymer, particularly for back sheets using polyethylene terephthalate film. These films contain several hundred parts of antimony used as a polymerization catalyst. For example, the research project conducted by the Netherlands Energy Research Centre and PV CYCLE (CU-PV) aims to develop and demonstrate alternatives to current applications. One example is using thermoplastics as encapsulants, which are easier to separate. Another is completely eliminating encapsulant use.

Silicon

Thinner cells can reduce the amount of silicon used in c-Si cells. For example, by switching to a rear-contact cell design, silicon use can be halved and energy consumption can be reduced by approximately 30% (Raithel, 2014). Silver. Covers approximately 6–8% of c-Si solar cells, approximately 95% of which are produced with printed silver contact lines on the front side. According to the International Technology Roadmap Research (ITRPV) study, a significant reduction in the amount of silver in cells is expected by 2018 (Raithel, 2014) because; recent advances in inkjet printing and printing technologies enable the use of other metals. The use of rear-contact or bifacial cells helps further reduce silver consumption per watt by increasing cell efficiency. For example, in a research project conducted by CU-PV, new metallization methods suitable for thinner semiconductors will be developed. These methods, by coating with seed layers covered by inkjet printing and subsequently plating with nickel and copper, provide silver savings of at least 99%. The silver components used in PV panels have been explained in more detail above. From a value perspective, silver is the most expensive component of c-Si panels per unit mass. It is followed by copper, silicon, aluminum, glass, and polymer (see Figure 2). The PV industry consumes 3.5–15% of global silver production. Higher figures in this range include production losses, while lower figures are derived from analysis of silver content in solar cells. On average, a typical c-Si panel contains approximately 6–10 grams of silver. Figure 3 shows recent silver consumption and future projections. New printing techniques and pastes have provided more than 30% silver savings between 2009–2012. Due to expected growth rates in the global PV industry, the Silver Institute predicts that silver consumption will increase in the medium and long term, with use per unit power further declining. While silver consumption per watt fell by two-thirds between 2013–2017, total silver consumption in 2017 is projected to equal 2013 levels. Silver contacts are approximately ten micrometers thick and face the sun. Additionally, the role of silver in solar panels is to provide electrical current flow in solar energy cells. Silver contacts are a thin layer applied to the surface of solar cells and enable the conversion of sunlight into electrical energy. Therefore, silver is an important component for the efficiency and performance of solar panels. However, due to the cost of silver and limited resources, the PV industry is seeking to reduce silver use and explore alternative materials. New printing techniques and advanced material use have helped reduce silver consumption. Additionally, technological advances and growth in the solar energy market support expectations that silver consumption per unit power will decline. Various new technologies have been applied for cells, back sheets, coatings, and sealing materials, resulting in more than 50,000 panel types. Tracking all materials for waste processing and recycling purposes is a challenging process and this challenge will continue. Creating global information flow systems with panel and material databases can facilitate achieving the goal of long-term waste management systems that maximize material recovery. The next section analyzes different waste management options for PV panels. The environmentally preferred approach is to repair a panel that has potentially reached end of service life and prepare it for reuse. Repair of PV panels (reuse) Most PV systems were installed in the past six years (from 15 GW in 2008 to 222 GW in 2015), meaning that today's expected average lifespan (30 years) sees 20 percent premature loss. If defects are detected in the early stages of the PV panel's life, customers can still claim warranty for repair or replacement if the contracting party exists. Insurance companies may intervene to compensate for part or all of the repair/replacement costs under the terms of contract agreements. In such cases, panel ownership typically transfers to the insurance company. Most defective panels are usually returned to the contracting party, a manufacturer's service partner, or the manufacturer for inspection and repair. Quality testing must be performed for a panel to be offered for sale through recycling to obtain some value in the used equipment market; these tests typically check electrical safety and power output. Flash test characterization and wet leak testing are examples of these. When repairs are necessary and possible, they typically include applications such as a new frame, new junction box, diode replacement, new plugs and sockets. Solar cells can even be replaced and panels can be re-laminated. This is done by companies offering 'B-spec' and 'C-spec' maintenance and repair services, which in some cases are sold to special projects. These services typically include regular maintenance work performed to improve panel performance and extend its service life.

Some basic steps for PV panel repair are as follows:

1. Detection of defective panel: Any defect affecting the panel's performance should be identified. This can be done through testing the panel's electrical properties and visual inspection. 2. Repair or replacement request: The owner of the defective panel can request repair or replacement according to warranty terms. Insurance companies may intervene to cover costs. 3. Panel return: The defective panel is usually returned to the manufacturer's service partner or the manufacturer. This step ensures the panel enters a detailed inspection and repair process. 4. Quality testing: The panel is subjected to quality testing upon return. These tests are performed to check the panel's electrical safety and power output. Flash test characterization and wet leak testing are just a few of these tests. 5. Repair operations: After defects in the panel are identified, necessary repair operations are performed. This may include applications such as a new frame, new junction box, diode replacement, replacement of plugs and sockets. Solar cells can even be replaced and panels can be re-laminated. 6. Retesting: After repair operations are completed, the panel is again subjected to quality tests. This is done to verify that the panel operates properly and delivers the desired performance. 7. Assembly: The panel is reassembled after repair operations are completed and it passes quality tests. This ensures the panel is safely and securely placed back in position. 8. Maintenance and monitoring: It is important to continue regular maintenance and monitoring processes for the panel after repair. This is done to optimize the panel's performance and ensure its long service life. In our next article, we will continue with the topic of decommissioning and processing (recycling) of PV panels. Wishing you good health.   Dr. Assoc. Prof. Cemil Koyunoğlu Department of Energy Systems Engineering Faculty of Engineering Yalova University