Imagine spending months designing a cutting-edge, high-efficiency bifacial solar module. You’ve selected the best N-type cells and the clearest glass, all to capture every possible photon from the front and the back. But what if a component as small as a wire were secretly casting a shadow, negating a significant portion of your hard-earned gains?
For many module manufacturers, this isn’t a hypothetical—it’s a hidden reality. The tiny metal ribbons connecting solar cells, a fundamental part of every module, can become one of the biggest obstacles to maximizing bifacial energy generation. Understanding and solving this challenge is key to unlocking the full potential of modern solar technology.
The Two-Sided Revolution: A Quick Look at Bifacial N-Type Modules
The solar industry is rapidly embracing N-type TOPCon (Tunnel Oxide Passivated Contact) cells for good reason. They offer higher efficiency and lower degradation than their predecessors. One of their most powerful features is their excellent bifaciality: the ability to generate electricity from light hitting both the front and rear sides.
This two-sided power generation, or „bifacial gain,“ is a game-changer for energy yield, especially in installations over reflective surfaces like white rooftops, sand, or snow. However, the rear side of the cell is incredibly sensitive to something we often overlook: internal shading.
The Unseen Obstacle: Meet the Interconnect Ribbon
To build a solar panel, individual cells must be wired together in series. This is done with thin strips of metal called interconnect ribbons, typically copper coated with solder. For decades, these ribbons have been flat—a simple and effective design for carrying electrical current from the front of one cell to the back of the next.
On a traditional, monofacial panel, the shadow cast by these ribbons on the front side was a known, calculated loss. But with bifacial modules, that same flat ribbon now casts a much more significant shadow on the rear side of the cell, directly blocking light that would otherwise generate power.
Quantifying the Shadow: Why Ribbon Geometry Matters
How much of a difference can a tiny ribbon make? The impact is staggering. Research and real-world testing show that conventional flat ribbons can block enough light to cause up to a 30% power loss on the rear side of the cell.
This happens because a flat, wide surface is the ideal shape for blocking light. Light reflecting off the ground toward the back of the module hits this flat barrier and is lost.
This reality has led innovators to rethink the fundamental shape of the interconnect. What if, instead of a flat ribbon, you used a round wire? A round wire has a much smaller profile for blocking direct light. Even better, its curved surface is excellent at capturing and reflecting scattered, off-angle light back onto the active cell area.
The theory is sound, but in manufacturing, theory isn’t enough. How can developers be certain that switching to a more complex—and potentially more expensive—round wire will deliver a worthwhile return on energy yield?
From Theory to Certainty: How to Test Ribbon Impact
The only way to get a definitive answer is to conduct a controlled experiment that isolates the one variable in question: the interconnect ribbon’s geometry. This is achieved through a precise A/B testing methodology.
At an applied research facility like PVTestLab, this process looks like this:
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Create Identical Twins: Two mini-modules or full-size prototypes are built using the exact same bill of materials (BOM). They use cells from the same batch, the same glass, the same encapsulant, and the same backsheet.
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Isolate the Variable: The only difference between the two modules is the interconnect. Module A is built with traditional flat ribbons. Module B is built with round wires. This is a core part of the solar module prototyping process.
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Process Under Real Conditions: Both modules are laminated and cured using the same industrial-grade equipment and process parameters that would be used in mass production. This ensures the results are transferable to a real factory floor.
With two perfectly matched modules prepared, it’s time for the moment of truth. Using a high-precision AAA Class flasher to illuminate and measure both sides of the module, a direct comparison can be made.
„By creating identical module twins that differ only by the interconnect, we provide manufacturers with undeniable data,“ notes Patrick Thoma, a PV Process Specialist at PVTestLab. „It’s no longer a simulation; it’s a direct, measurable comparison of how a specific material choice will perform in a finished product.“
This type of bifacial performance analysis delivers clear, quantifiable data: Module A produced X watts on the rear side, while Module B produced Y watts. The difference between X and Y reveals the real-world impact of the interconnect choice.
The Data-Driven Decision for Manufacturers
Armed with this reliable data, module developers and material suppliers can make informed decisions. They can calculate the precise increase in bifacial gain and weigh it against any changes in material cost or process complexity.
This approach de-risks innovation. Instead of investing heavily in a new material based on datasheets and simulations, companies can validate performance using a small batch of prototypes, ensuring that when they scale up, the results will match their expectations.
Frequently Asked Questions (FAQ)
What exactly is an interconnect ribbon?
An interconnect ribbon is a thin, solder-coated copper conductor used to electrically connect individual solar cells together to form a string, which is then assembled into a complete solar module.
What is „bifacial gain“?
Bifacial gain is the extra energy generated by the rear side of a bifacial solar module compared to the energy generated by the front side alone. It is typically expressed as a percentage. For example, a 10% bifacial gain means the module produces 10% more energy than a monofacial module of the same front-side power rating under the same conditions.
Why is rear-side shading a bigger deal for N-type modules?
N-type cells, especially TOPCon and HJT designs, have exceptionally high bifaciality (often 80-95%), meaning their rear side is nearly as efficient as their front side. This makes any shading on the rear side cause a much more significant absolute power loss compared to older technologies with lower bifaciality.
Are round wires the only solution?
No, round wires are just one example of an optimized interconnect geometry. Other solutions include multi-busbar designs with very thin, round wires, and other proprietary ribbon shapes designed to minimize shading and maximize light capture. The key principle is moving away from wide, flat conductors on the rear of the cell.
Your Next Step in Module Optimization
The performance of a modern solar module is a story of millimeters and percentage points. As this example shows, even the smallest components can have an outsized impact on overall energy yield. The key to leading the market is not just having innovative ideas, but also having a reliable, data-driven way to prove they work.
If you’re exploring new materials or module designs, the best way to understand their true impact is to test them under real-world industrial conditions. To see how a structured A/B test could validate your next innovation, consult with a process specialist to map out a plan that fits your goals.