1. Introduction
Photovoltaic (PV) ribbon, though a small component, serves as the critical “circulatory system” of solar modules, responsible for collecting and transmitting electrical current. Its performance directly determines the power output efficiency and long-term reliability of the entire module. In the early stages of the photovoltaic industry, round wires were once used for cell interconnection. However, with technological advancements and the demand for large-scale production, flat ribbons have become the absolute mainstream. The competition between these two forms reflects the industry’s relentless pursuit of higher efficiency, lower costs, and greater reliability. As a buyer, should we choose round wire or flat wire? This article will provide a detailed comparison of the differences between round and flat wires from multiple perspectives, which can help you learn more about round wire and flat wire.
2. Structural Differences
The most fundamental difference between round wire and flat wire ribbons lies in their cross-sectional geometry:
2.1 Round wire ribbons have a circular cross-section. Their geometry offers structural robustness and flexibility. Because of their shape, they tend to occupy less horizontal space but extend vertically when laid on a solar cell.
2.2 Flat wire ribbons have a rectangular or flattened cross-section. They present a wider surface area, which increases the electrical conduction pathway and reduces resistive losses.
This difference in shape has cascading implications for optical shading, soldering area, and module design optimization.
3. Manufacturing Process Differences
3.1 Round Wire Ribbon Manufacturing by Solar PV Ribbon Machine
The production of round wire ribbons is relatively straightforward:
3.1.1 Drawing Copper Rods: High-purity copper rods are drawn into wires with circular cross-sections.
3.1.2 Surface Cleaning: The wires undergo degreasing and oxide removal to prepare them for coating.
3.1.3 Coating: A layer of tin, tin-lead alloy, or silver is applied via electroplating or hot-dipping, enhancing solderability.
3.1.4 Rewinding and Packaging: The finished wires are wound onto spools and prepared for delivery.
Round wire ribbons do not require additional shaping, making their process simpler and less costly.
3.2 Flat Wire Ribbon Manufacturing by Solar PV Ribbon Machine
Flat wire ribbons require more precision:
3.2.1 Drawing Copper Rods: Similar to round wires, the starting point is drawn copper wire.
3.2.2 Rolling or Calendering: The wire is mechanically flattened using rolling mills to achieve the required width and thickness. Maintaining consistent dimensions is critical.
3.2.3 Surface Treatment and Coating: The flattened wire is plated with tin or silver to improve soldering quality and corrosion resistance.
3.2.4 Tension Control and Rewinding: Flat wires are prone to twisting or warping, so stress management during winding is essential.
The extra rolling process and precision control add to the cost and complexity compared to round wires.
4.Performance Differences
4.1 Electrical Properties
4.1.1 Flat wire ribbons provide lower resistance due to their larger cross-sectional area relative to volume.
4.1.2 This results in more efficient current flow and reduced energy losses, making them better suited for high-efficiency modules.
4.1.3 Round wire ribbons, while sufficient for conventional modules, do not perform as well when extremely low resistive losses are required.
4.2 Optical Properties
4.2.1 Shading is a critical concern in solar cell design. Round wires cast circular shadows that block a greater fraction of light.
4.2.2 Flat wires cast thinner, more uniform shadows. Moreover, flat wires can be designed with reflective coatings that redirect part of the incoming sunlight back into the solar cell, thereby reducing shading losses and enhancing energy yield.
4.2.3 For bifacial and transparent-backsheet modules, this optical advantage makes flat wires the preferred option.
4.3 Mechanical Properties
4.3.1 Round wires exhibit excellent flexibility and tensile strength, making them resistant to bending and mechanical fatigue.
4.3.2 This property makes them highly suitable for flexible solar panels that need to bend or roll.
4.3.3 Flat wires, in contrast, provide good tensile strength but are more vulnerable to twisting and edge cracking, especially during handling and soldering.
4.4 Solderability
4.4.1 Flat wires have a larger contact surface with solar cells, creating stronger and more consistent solder joints.
4.4.2 This improves long-term reliability under thermal cycling.
4.4.3 Round wires are easier to position and align during soldering but may suffer from smaller bonding areas, which can sometimes weaken solder joints.
| Performance Aspect | Round Wire Ribbon | Flat Wire Ribbon |
| Electrical Performance | Slightly higher resistance but sufficient for conventional modules | Lower resistance, superior conductivity |
| Optical Performance | Higher shading ratio, leading to some light loss | Lower shading ratio, improves light capture |
| Mechanical Properties | Good flexibility, easy to bend and assemble | Stiffer, may require careful handling |
| Thermal Stability | Stable in standard soldering conditions | More uniform thermal distribution due to larger surface |
| Cost Considerations | Lower manufacturing cost, mature process | Higher cost due to complex processing |
5. Application Differences
5.1 Round Wire Applications
5.1.1Conventional crystalline silicon modules: Their robustness and lower cost make them suitable for mainstream production.
5.1.2 Flexible solar panels: Their flexibility and mechanical resilience allow them to withstand bending without breaking.
5.2 Flat Wire Applications
5.2.1 High-efficiency monocrystalline modules (e.g., PERC): Reduced resistance and shading loss contribute directly to higher power output.
5.2.2 Bifacial modules: Optical advantages maximize both front- and rear-side energy harvesting.
5.2.3 Glass-glass and transparent backsheet modules: Their ability to reflect light into the cell improves utilization of transmitted light.
6. Process and Cost Differences
6.1 Round wires benefit from simple manufacturing and relatively low production costs. They are easier to produce in bulk with consistent quality.
6.2 Flat wires, while offering performance advantages, demand higher precision in rolling and tension control. This makes their manufacturing more capital-intensive and costly. For module producers, the choice often comes down to balancing cost and performance requirements.
7. Summary of Differences:
| Feature | Flat Ribbon | Round Wire |
| Contact Area | Large(Surface contact) | Small(Line contact) |
| Series Resistance | Low | High |
| Shading Loss | Slightly Higher(but mitigated by MBB) | Theoretically Lower |
| Mechanical Strength | High(Strong adhesion) | Low(Poor adhesion, prone to fail) |
| Production Speed | Very High(Fully automation) | Low(Difficult to automate) |
| Reliability | High(Excellent stress distribution) | Low(Stress concentration) |
| Main Application | All mainstream technologies(PERC, TOPCon, HJT) | Niche applications(e.g., some shingled modules) |
8.Conclusion
Round wire and flat wire PV ribbons each offer distinct strengths and weaknesses. Round wires remain valuable for conventional and flexible solar applications due to their mechanical robustness and cost-effectiveness. Flat wires, with superior electrical and optical properties, are becoming the standard in high-efficiency and bifacial modules.The decision to use round or flat wire depends largely on the design priorities of the solar module—whether the focus is on minimizing cost, maximizing efficiency, or enabling flexibility. If you want learn more about Solar PV Ribbon Machine, you can click here.
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