This is a great question and crucial for proper string sizing to avoid over-powering your optimizers and inverter. Here's the breakdown

You should use the FRONT STC (410W) for your SolarEdge STRMAX calculations.

Here's why: SolarEdge Optimization Focus

SolarEdge optimizers are designed to maximize power extraction from each module, considering its individual output. They don't sum the potential output from the front and back simultaneously to optimize. The optimizer is primarily concerned with the front-side power generation.

STRMAX Calculation Logic

The maximum string length (STRMAX) is fundamentally about not exceeding the DC input power limits of the optimizers. SolarEdge's STRMAX calculation formula specifically considers the single module power in its denominator. They are not accounting for the possibility of bifacial gain when calculating STRMAX.

Conservative Approach & Safety Margin

String sizing needs to be conservative to account for variations in module output, temperature coefficients, and real-world conditions. Using the front STC power rating provides a safety margin.

Flush-Mounted Bifacial Modules

Given your low-slope, flush-mounted configuration, the backside contribution will be minimal. The design will effectively be acting as though it is a monofacial install.

Datasheet Emphasis

SolarEdge documentation, string calculators, and training materials predominantly refer to the front-side STC power when calculating string lengths.

In Summary

You should base your SolarEdge STRMAX calculations on the

FRONT STC (410W) rating of your Sirius ELNSM54M-HC-410 modules.

Important Considerations



Bifacial Gain Impact

While not relevant for STRMAX, remember the bifacial gain will contribute to overall system yield. Don't disregard it entirely when considering system performance and ROI. It's an extra benefit.

SolarEdge Design Tools

Use the official SolarEdge Designer software or string sizing calculator on their website. It usually has built-in module databases and helps ensure you stay within all electrical limitations.

Consult SolarEdge Directly (Optional but Recommended): If you want absolute certainty, contact SolarEdge technical support and clarify your specific situation. They can provide definitive guidance based on your inverter model, optimizer selection, and module choice.By using the front STC power (410W) for STRMAX calculations, you'll ensure your strings are sized appropriately for your SolarEdge system and avoid any risk of overloading the optimizers. Flag for review