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Optimizing Solar Strings: Understanding and Solving Module Mismatch
At Autarco, our goal is to ensure every solar energy system delivers maximum performance, safety, and value for its entire lifetime. A key aspect of achieving this is understanding how individual components work together, especially the solar modules within a string.
This article explains a common challenge in solar design—module mismatch—and details the modern technology used to solve it.
This article explains a common challenge in solar design—module mismatch—and details the modern technology used to solve it.
The Challenge: Why Mixing Different Modules on a String Causes Power Loss
In a typical solar installation, modules are connected in a series to form a "string," which then feeds into an inverter. In a standard string, a fundamental rule of physics applies: the entire string can only operate at one single current.
This current is dictated by the lowest-performing module in the string. If you have modules with different current ratings (Imp) on the same string—due to being different models, from different manufacturing batches, or even due to one panel being slightly shaded or soiled—a "drag-down" effect occurs.
This creates two significant problems:
In a typical solar installation, modules are connected in a series to form a "string," which then feeds into an inverter. In a standard string, a fundamental rule of physics applies: the entire string can only operate at one single current.
This current is dictated by the lowest-performing module in the string. If you have modules with different current ratings (Imp) on the same string—due to being different models, from different manufacturing batches, or even due to one panel being slightly shaded or soiled—a "drag-down" effect occurs.
This creates two significant problems:
- Immediate Power Loss: A module rated for a higher current is forced to operate at the lower current of its neighbors. It is no longer performing at its Maximum Power Point (MPP), leading to a direct and significant loss of energy generation. The power that the stronger module could have produced is simply lost.
- Long-Term Performance Risks: A severe mismatch in current forces modules to operate under electrical stress. In the lower-current modules, cells can be forced into a state of reverse bias, consuming power instead of producing it. This energy is dissipated as heat, creating hot spots. Over time, this elevated temperature can lead to:
- Uneven Degradation: The hotter, stressed modules will degrade faster than their neighbors.
- Increased Risk: This degradation worsens the mismatch, creating a negative feedback loop that can impact the long-term performance and safety of the entire system.
For these reasons, the long-standing best practice has been to never mix different modules on the same standard string.
Optimizers as a workaround
When maintaining a perfectly matched string is not feasible—for example, during a repair where the original module is no longer available—the priority shifts to mitigating the inevitable power loss. This is where Module-Level Power Electronics (MLPE), such as optimizers, offer a feasible workaround.
When maintaining a perfectly matched string is not feasible—for example, during a repair where the original module is no longer available—the priority shifts to mitigating the inevitable power loss. This is where Module-Level Power Electronics (MLPE), such as optimizers, offer a feasible workaround.
An optimizer is a device attached to an individual solar module that manages its output. By performing Maximum Power Point Tracking (MPPT) for its specific module, it electronically "decouples" it from the others. This allows the optimizer to manage the mismatch and recover a significant portion of the energy that would have otherwise been lost.
While effective at salvaging power, it's important to view optimizers as a tool for managing a compromised situation, not as a replacement for a clean initial design.
Optimizers can be added for an Autarco system in the remote survey, in the tab "optimizers" or simply added in the additional items. Tigo TS4A-O can be found in the Autarco's offer. This solution has been installed and tested for numerous Autarco's system and is simply the best for module mismatch and module shading.