What if the very wires connecting your solar cells were secretly stealing a portion of their power? It sounds counterintuitive, but for bifacial solar modules—the workhorses that capture sunlight from both sides—this is a daily reality. A significant portion of the energy boost from the rear side is lost before it’s ever generated—all because of tiny shadows cast by the module’s internal wiring.
This isn’t a minor detail. As the solar industry pushes for every fraction of a percent in efficiency, understanding these „hidden“ losses is critical. It turns out, the shape of the interconnect ribbons connecting the cells plays an outsized role in how much extra energy your bifacial module can actually produce. Let’s dive into why this happens and what the data tells us about making a smarter choice.
Understanding Bifacial Gain and Its Arch-Nemesis: Internal Shading
A bifacial solar module is a brilliant piece of engineering. While the front side captures direct sunlight, the rear side absorbs reflected and scattered light from the ground (known as albedo). This extra power is called „bifacial gain,“ and it can increase a module’s total energy output by anywhere from 5% to 30%, depending on the installation environment.
But here’s the catch: for that reflected light to reach the rear side of the solar cell, it must first pass through the module’s backsheet or back glass. And lying in its path are the electrical conductors—the ribbons and busbars that collect the generated current.
These components, though essential, cast shadows on the back of the cells. This phenomenon, known as internal shading, directly reduces the amount of light reaching the active cell area, chipping away at your potential bifacial gain. The wider and more opaque these components are, the larger the shadow they cast and the greater the energy loss.
The Two Contenders: Flat Busbars vs. Round Wires
For years, the standard for cell interconnection has been the flat, rectangular busbar. It’s a proven, cost-effective method for carrying electrical current. However, from an optical perspective, its geometry is far from ideal for a bifacial module. Its wide, flat profile creates the largest possible shadow for its size, blocking a significant amount of light from reaching the cell’s rear surface.
Enter the modern alternative: round wires. While serving the same electrical function, their cylindrical shape changes the game entirely.
A round wire doesn’t block light in the same way a flat ribbon does. Its curved surface allows a significant portion of scattered light to pass around it and still hit the cell. Think of it like the difference between holding a large, flat book over a surface versus a thin pencil. The pencil’s shadow is much less pronounced because light can bend around its narrow, curved profile.
Putting It to the Test: From Optical Models to Physical Prototypes
At PVTestLab, we don’t rely on theory alone. Our mission is to bridge the gap between simulation and real-world manufacturing. To quantify the impact of interconnect geometry, we conducted a two-stage analysis.
First, we used high-resolution optical modeling to simulate the rear-side irradiance on a solar cell behind both a traditional flat busbar and a modern round wire. The results were striking:
- Flat Busbar: The model predicted a rear-side irradiance loss of 15.6% due to the shadow cast by the ribbon.
- Round Wire: The same model showed only a 6.2% loss—a relative improvement of over 60%!
This simulation gave us a powerful hypothesis, but the real proof comes from physical validation. The next step was to move from the computer to our R&D production line. Creating real-world modules with our solar module prototyping capabilities allowed us to measure their actual performance under controlled conditions. The physical prototypes confirmed the simulation’s findings, demonstrating a measurable increase in bifacial gain for the module built with round wires. This process of testing, validating, and optimizing is what turns a good idea into a bankable product.
What This Means for Your Module Design
Choosing between interconnect technologies isn’t just a matter of picking a component; it’s a strategic decision that directly impacts your module’s Levelized Cost of Energy (LCOE). While round wires might involve different manufacturing processes or materials, the potential for a significant boost in bifacial gain often outweighs the initial investment.
For module developers, this data highlights a key area for optimization. It’s a reminder that every component, no matter how small, contributes to the final energy yield. A thorough process of structured material testing and lamination trials is essential to ensure that your chosen interconnects, encapsulants, and cells work together effectively to maximize performance and long-term reliability. The geometry of a wire is a perfect example of how small design changes can unlock significant performance gains.
Your Questions on Interconnect Shading, Answered
What exactly is „bifacial gain“?
Bifacial gain is the additional energy produced by the rear side of a bifacial solar module compared to a standard monofacial module under the same conditions. It’s expressed as a percentage. For example, a 10% bifacial gain means the module produced 10% more energy than its front-side-only equivalent.
Is internal shading the only factor affecting bifacial performance?
No, it’s one of several important factors. The most critical external factor is the „albedo,“ or reflectivity of the surface beneath the modules (e.g., white gravel has a high albedo, while grass has a low one). The module’s installation height and tilt angle also play a huge role in how much light reaches the rear side. However, internal shading is one of the few factors you can control directly at the design and manufacturing stage.
Are round wires more expensive than flat busbars?
There can be differences in material cost and the complexity of the manufacturing process (e.g., the stringer equipment used). However, many manufacturers find that the increase in energy yield and the resulting lower LCOE provide a clear return on investment, making the technology highly competitive.
How can I test which interconnect is best for my specific module design?
The most reliable way is through controlled prototyping and testing. By building identical modules that differ only in their interconnection technology, you can perform head-to-head comparisons of electrical performance (I-V curves), durability, and bifacial gain. This data-driven approach removes uncertainty and validates your design choices before scaling up to mass production.
Beyond the Wires: The Future of Module Optimization
The lesson from comparing flat busbars and round wires is simple: in solar module design, every detail matters. What was once a standard, unquestioned component can become a major lever for improving performance and competitiveness.
As technology continues to advance, from new encapsulant materials to innovative cell structures, this holistic approach to design and validation will become even more critical. The most successful innovators will be those who rigorously test, measure, and optimize every single element of their modules.
If you’re exploring new module designs or seeking to optimize an existing product, understanding these nuances is your first step toward building a better, more efficient solar future. If you’re ready to move from theory to practice, you can discuss your R&D goals with an expert who can help you navigate the complexities of module development.