As the global demand for renewable energy sources intensifies, solar power has emerged as a pivotal solution due to its sustainability and minimal environmental impact. Among various technologies, crystalline silicon photovoltaic panels dominate the market, accounting for a significant share of installed capacity. However, the lifespan of these solar panels is typically 20–30 years, leading to an impending surge in waste photovoltaic modules. By 2030, it is projected that millions of tons of decommissioned photovoltaic panels will accumulate globally, posing severe environmental risks and resource wastage if not managed properly. The core challenge in recycling these panels lies in the separation of laminated components, which include layers such as the cover glass, ethylene-vinyl acetate (EVA) encapsulant, silicon cells, and backsheet, all tightly bonded together. Traditional methods like thermal and chemical separation often result in secondary pollution or low efficiency, underscoring the need for innovative mechanical approaches. In this study, we focus on developing a mechanical separation equipment designed to efficiently disassemble waste crystalline silicon photovoltaic panels, aiming to enhance recycling rates, reduce costs, and minimize environmental footprint. We present a comprehensive design, fabrication, and testing process, supported by formulas and tables to quantify performance and economic viability.
The structure of a typical crystalline silicon photovoltaic panel consists of multiple layers: an aluminum frame, junction box, cover glass, EVA encapsulant, silicon solar cells, and a backsheet, all adhered using specialized sealants. The composition by mass fraction for a standard 1-ton batch of photovoltaic panels is summarized in Table 1. This layered configuration makes separation difficult, as the EVA acts as a strong adhesive, requiring precise mechanical intervention to avoid damage to valuable materials like silicon and glass. Our equipment targets the separation of the cover glass from the remaining laminated components, which is critical for enabling downstream recycling processes such as silicon purification and glass reuse.
| Component | Mass (kg) | Mass Fraction (%) |
|---|---|---|
| Cover Glass | 700.00 | 70.000 |
| Aluminum Frame | 180.00 | 18.000 |
| EVA | 51.00 | 5.100 |
| Silicon Cells | 36.50 | 3.650 |
| Backsheet | 15.00 | 1.500 |
| Cables | 10.00 | 1.000 |
| Aluminum (other) | 5.30 | 0.530 |
| Copper | 1.14 | 0.114 |
| Silver | 0.53 | 0.053 |
| Other Metals (e.g., Sn, Pb) | 0.053 | 0.053 |
To address the separation challenge, we formulated a recycling process flow for waste crystalline silicon photovoltaic panels, as illustrated in Figure 1. The process begins with manual removal of the aluminum frame and junction box, followed by mechanical separation of the laminated components using a custom-designed equipment. This equipment comprises several modules: a roller conveyor mechanism, a cutting tool and separation unit, and a transmission system. Each module was designed with precision to handle standard photovoltaic panel dimensions, such as 1980 mm × 980 mm for a 245 Wp panel, and to operate under controlled conditions to maximize efficiency and minimize residue. The integration of heating elements, for instance, softens the EVA layer, facilitating cleaner separation. Our approach emphasizes modularity, allowing for scalability and adaptation to various photovoltaic panel types.
The roller conveyor mechanism is a critical component for transporting photovoltaic panels through the separation process. Given that a single photovoltaic panel weighs approximately 28 kg and measures 1980 mm in length and 980 mm in width, the roller design must ensure stable and efficient movement. The length of the rollers is determined by the formula: $$ L = W + \Delta B $$ where \( L \) is the roller length, \( W \) is the panel width (980 mm), and \( \Delta B \) is the width allowance (10 mm), resulting in \( L = 990 \) mm. The roller diameter is calculated based on torsional stress and power transmission requirements. The torque and power equations are: $$ d \geq \sqrt[3]{\frac{9.55 \times 10^6 \cdot p}{0.2 [\tau] n}} $$ and $$ p = \mu G V $$ where \( d \) is the roller diameter, \( [\tau] \) is the allowable torsional stress for steel (30 MPa), \( n \) is the rotational speed, \( p \) is the transmitted power, \( \mu \) is the friction coefficient (0.25), \( G \) is the panel mass, and \( V \) is the linear velocity. Additionally, the maximum stress on the roller is given by: $$ \sigma_{\text{max}} = \frac{M_{\text{max}}}{\frac{\pi}{32} d^3 \left[1 – \left(\frac{d_n}{d}\right)^4\right]} $$ where \( M_{\text{max}} \) is the maximum bending moment and \( d_n \) is the inner diameter. Based on these calculations, we selected rollers with a diameter of 60 mm, thickness of 2 mm, and spacing of 100 mm to ensure durability and smooth operation, even under frequent start-stop conditions common in recycling processes.
For the cutting tool and separation mechanism, we designed a specialized unit to precisely separate the cover glass from the EVA and other layers. The EVA layer thickness typically ranges from 0.2 mm to 0.8 mm, necessitating a tool that can cleanly cut without causing excessive damage. The cutting tool, made from high-speed steel for its strength and sharpness, has a thickness of 15 mm to ensure complete separation. The tool geometry includes a front angle \( \gamma = 73^\circ \) to reduce cutting forces and a wedge angle of \( 17^\circ \) to direct chips away from the workpiece. The rear angle is set to \( 0^\circ \) to enhance durability and ensure the cover glass exits smoothly after separation. The tooltip radius is optimized using the formula: $$ R_y = \frac{f^2}{8 R_\varepsilon} $$ where \( R_y \) is the maximum surface roughness height, \( R_\varepsilon \) is the tooltip radius (0.15 mm), and \( f \) is the feed rate. This results in a precise cut with minimal residue. The cutting mechanism employs a modular design with 10 independent units, each 105 mm long, to handle the full width of the photovoltaic panel. This is coupled with a screw lift system (model SWL1T, ratio 1:24, stroke 300 mm) and linear guides (SBR30S2 + 650L) to manage loads up to 330 N, ensuring stability during the cutting process.
The transmission system powers the entire operation, with a focus on achieving variable cutting speeds for different photovoltaic panel conditions. The required power for cutting is derived from: $$ P_{\text{cut}} = P_{\text{motor}} \cdot \eta_1 \eta_2 \eta_3 \eta_4 $$ where \( P_{\text{motor}} \) is the motor power (750 W), and \( \eta_1 \), \( \eta_2 \), \( \eta_3 \), and \( \eta_4 \) are efficiencies of the reducer (0.96), chain drive (0.96), bearings (0.98), and friction transmission (0.88), respectively. This gives \( P_{\text{cut}} \approx 600 \) W. To achieve a cutting speed range of 0–2 m/min, we incorporated a frequency converter (model AS2-107) that adjusts the motor speed based on: $$ \frac{P_1}{P_2} = \left(\frac{n_1}{n_2}\right)^3 $$ where \( P_1 \) and \( P_2 \) are the power at adjusted and base frequencies, and \( n_1 \) and \( n_2 \) are the corresponding speeds. The motor speed is calculated as \( n_0 = \frac{60 f}{p} \), with \( p \) as the pole pairs and \( f \) as the frequency. Bearings (UCT205) support the rollers for bidirectional movement, essential for the reciprocating cutting action. This system ensures efficient handling of photovoltaic panels during separation, with minimal energy consumption.
We fabricated a first-generation prototype of the mechanical separation equipment, integrating all modules into a cohesive unit. The operational workflow involves placing de-framed photovoltaic panels onto the roller conveyor, where they are heated to 100–140°C using integrated heating elements to soften the EVA layer. The panels then advance to the cutting unit, where the cover glass is separated from the remaining laminated components. The separated glass is conveyed out via a rear mechanism, while the residual layers (EVA, cells, backsheet) are collected below for further processing. This design emphasizes automation and scalability, with potential for integration into large-scale recycling facilities for photovoltaic panels.
To evaluate the equipment’s performance, we conducted separation tests on 10 waste crystalline silicon photovoltaic panels, each rated at 245 Wp. The panels were processed according to the established workflow, and key metrics such as separation efficiency, residue rate, and EVA film thickness were measured. The average separation time per photovoltaic panel was 2.45 minutes, achieved by controlling the cutting speed through the frequency converter. The residue on the cover glass surface, primarily EVA, was quantified using image analysis and thickness gauges. Results showed an average residue rate of 6.48% and an average residual EVA film thickness of 0.074 mm, indicating high separation quality. These outcomes demonstrate the feasibility of mechanical separation for recycling photovoltaic panels, with minimal material loss and no secondary pollution. The efficiency can be further optimized by refining the heating parameters and tool geometry in future iterations.
The economic viability of recycling waste photovoltaic panels is a crucial consideration for widespread adoption. We analyzed the costs associated with the mechanical separation process, focusing on energy consumption, equipment depreciation, and operational expenses. For a standard 245 Wp photovoltaic panel, the separation cost per unit is calculated using: $$ p_1 = \frac{(P_{\text{motor}} + P_{\text{heating}} + P_{\text{sensors}}) \times 16 \times p_{\text{electricity}} + \frac{p_{\text{equipment}}}{t}}{16 \times \frac{60}{t_{\text{processing}}}} $$ where \( P_{\text{motor}} = 750 \) W, \( P_{\text{heating}} = 1200 \) W, \( P_{\text{sensors}} = 500 \) W, \( p_{\text{electricity}} \) is the local electricity rate, \( p_{\text{equipment}} \) is the prototype cost, \( t \) is the equipment lifespan (20 years), and \( t_{\text{processing}} \) is the processing time per panel (2.45 minutes). Assuming a two-shift operation (16 hours daily), the cost per panel is approximately $0.224. This low cost, combined with the value of recovered materials like silicon, glass, and metals, makes mechanical separation economically attractive. For instance, silicon can be purified and reused in new photovoltaic panels, while glass can be refurbished or recycled in construction. A breakdown of recoverable materials from 1 ton of multicrystalline and monocrystalline silicon photovoltaic panels is provided in Table 2, highlighting the potential revenue streams.
| Material | Multicrystalline Silicon (kg) | Monocrystalline Silicon (kg) |
|---|---|---|
| Glass | 700 | 700 |
| Aluminum | 185.3 | 185.3 |
| Silicon | 36.5 | 36.5 |
| EVA | 51 | 51 |
| Copper | 1.14 | 1.14 |
| Silver | 0.53 | 0.53 |
| Other Metals | 0.053 | 0.053 |
In addition to cost savings, the environmental benefits of mechanical separation are significant. Unlike thermal methods that may release harmful gases or chemical processes that generate liquid waste, our approach produces no secondary pollutants. The equipment’s modular design allows for easy maintenance and upgrades, further enhancing its sustainability. For example, the cutting tools can be sharpened or replaced without disassembling the entire unit, reducing downtime. Moreover, the use of energy-efficient components, such as the frequency converter, minimizes the carbon footprint of the recycling process. As the photovoltaic industry continues to grow, adopting such eco-friendly technologies will be essential for achieving circular economy goals.
Despite the promising results, we identified areas for improvement during testing. For instance, some photovoltaic panels exhibited warping during heating, which could affect separation uniformity. To address this, future work could involve thermal field analysis to optimize heating distribution and prevent deformation. Additionally, increasing the automation level, such as integrating robotic arms for panel handling, could boost efficiency and reduce labor costs. We also plan to explore adaptive control systems that adjust cutting parameters in real-time based on panel thickness and condition, further enhancing residue reduction. These advancements could make mechanical separation even more competitive with conventional recycling methods for photovoltaic panels.
In conclusion, our research demonstrates the effectiveness of mechanical separation equipment for recycling waste crystalline silicon photovoltaic panels. The designed equipment achieves high separation efficiency with minimal residue, offering a cost-effective and environmentally friendly solution. Key findings include an average separation time of 2.45 minutes per panel, a residue rate of 6.48%, and a processing cost of $0.224 per unit. By leveraging modular design, precise engineering, and economic analysis, this approach supports the sustainable management of end-of-life photovoltaic panels, contributing to the broader adoption of solar energy. Future efforts will focus on optimizing the system for industrial-scale applications, ultimately fostering a closed-loop lifecycle for photovoltaic technologies.