Optimizing Solar Cell Manufacturing: Thermal Quality Checks for Soldering, Tabbing, and Stringing
Detecting Improper Soldering in Solar Modules Through Hotspot Identification
Challenge
Identifying soldering defects in solar modules is challenging because traditional electrical resistance checks cannot pinpoint exact fault locations. Using thermal paper is labor-intensive and lacks precise fault localization, complicating effective quality assurance in the delicate soldering, tabbing, and stringing processes of photovoltaic cell manufacturing.
Solution
The solution involves applying high-intensity illumination during end-of-line testing, capturing thermal responses with an infrared camera. This method precisely detects hotspots resulting from increased internal resistance due to defective soldering, tabbing, or stringing, immediately highlighting faults and missing connections, thus ensuring accurate fault localization in solar panels.
Benefits
- Immediate identification of soldering faults, minimizing production downtime and repair delays.
- Enhanced manufacturing consistency through precise thermal detection of subtle soldering imperfections.
- Improved reliability by ensuring only properly connected photovoltaic cells advance through production.
- Detailed long-term quality analysis using comprehensive thermal snapshots for ongoing process refinement.
- Reduction of defective solar modules, resulting in higher efficiency and reduced production costs.
Thermal Quality Checks of Soldering, Tabbing, and Stringing of Solar Cells
The current standard technique for manufacturing solar photovoltaic modules involves two side-contacted cells and has been widely adopted. This method begins by interconnecting individual cells into strings through soldering ribbons from the front contacts of one cell (tabbing) to the back contacts of the neighboring cell (stringing). These strings are then interconnected and laminated between a transparent glass or polymer front sheet and a glass, metal, or polymer back sheet using an encapsulation material.
Today, most solar module manufacturers utilize automatic solar cell soldering. This automation ensures more consistent quality, reduces breakages, and allows for the use of thinner solar cells. The soldering process is critical, as it enables the photovoltaic module to effectively transmit electricity.
The precision of automatic soldering extends beyond reliability; it pushes the boundaries of technology. By minimizing human error, ensuring uniformity, and reducing the likelihood of defects, automatic soldering drives the industry towards thinner and more efficient cells. This advancement not only enhances the performance of solar modules but also reduces manufacturing costs, marking an exciting era for the solar energy industry.
The wiring on top of the solar cell is delicate and thin, designed to expose as much of the solar cell surface area as possible. However, these wirings must maintain high quality to ensure low impedance. The soldering process for these thin wires is challenging and requires frequent checks before an additional protective layer is applied.
Electrical resistance measurements can indicate if the overall impedance is out of specification, but they do not reveal the fault’s location. Since high impedance generates heat, the conventional fault-checking procedure uses thermal paper, which changes color in response to temperature changes to locate the fault. However, this method is labor-intensive and lacks precision in identifying the exact failure location.
Advanced Thermal Inspection for Faulty Soldering, Tabbing, and Stringing of Photovoltaic Modules
In the production of solar panels, each module undergoes a final quality check to determine performance and identify potential issues due to faulty soldering, tabbing, or stringing.
This application places an infrared (IR) camera next to a steady sun simulator. As an end-of-line test, the solar cell test involves applying high-intensity light to the solar panel and measuring its heat response. The modules are exposed to bright light from above. The IR camera installed parallel to the light source, uses optics with a 33° horizontal opening angle to detect the entire PV panel. For best thermal contrast, to evaluate the hot spots precisely, the module is used in short circuit mode.
When light hits the solar cell, it excites electrons in the semiconductor, creating a flow of electric current. The tabbing and stringing conduct this current to external interfaces. If the soldering process is not optimal, tabbing is insufficient, or stringing is broken, the internal resistance of these electrical connections increases. During the end-of-line test, higher resistance at faulty points leads to a temperature rise or no thermal increase if the connection is completely interrupted.
During illumination, the IR camera takes a snapshot to analyze the solar panel for hotspots and missing interconnections using the Event Grabber feature of the PIX Connect software. If an area is too hot or parts are missing, an alarm informs the operator, and the snapshot is stored. By verifying performance, only cells meeting quality standards are integrated into modules.
Thermal Alerts and Long-Term Analysis improve Solar Panel Tabbing, Stringing, and Soldering Manufacturing Quality
In this application, thermal accuracy, resolution, and measurement field of view (MFOV) are crucial for detecting small soldering issues in solar modules. High thermal accuracy ensures that even the slightest temperature variations, indicative of potential faults, are detected. High spatial resolution allows for detailed imaging, making it possible to identify tiny imperfections in the soldering process that might otherwise go unnoticed.
When the operator or the programmable logic system is alerted to an excessively warm area, production can be halted to identify and eliminate the source of the failure. Since its implementation, this proactive approach has significantly increased the output of high-quality products. This system allows for immediate response to potential issues, preventing defective products from continuing down the production line and reducing the risk of larger-scale problems.
Additionally, continuous updates on quality trends enable timely adjustments and improvements in the production process, ensuring consistent quality and efficiency. By saving and storing snapshots of all faulty panels, manufacturers can conduct long-term analyses of thermal data. Each thermal snapshot provides comprehensive radiometric data, meaning the temperature of every single pixel is recorded and available for detailed analysis. This extensive data can be used for hotspot analysis, pinpointing areas prone to overheating, or to create detailed temperature profiles, which offer insights into the overall heat distribution across the panels.
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Talk to us about your IR Temperature Measurement Requirements
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