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How to Estimate Bifacial Gain: A Comprehensive Guide for Utility-Scale Solar Design


Bifacial solar modules are transforming the utility-scale solar landscape by significantly increasing energy yield and system efficiency. However, accurately determining bifacial gain requires sophisticated modeling and precise weather data. Here’s a detailed look at the methodology and tools used to calculate bifacial gain and optimize system design.

Types of Bifacial Gain


  1. Maximum Bifacial Gain

This is the theoretical maximum power boost achievable under ideal conditions. It’s calculated using weather data and simulations, such as with the System Advisor Model (SAM), and represents the best-case scenario.


  1. Actual Bifacial Gain

This reflects real-world energy yield, accounting for additional losses like shading, structural factors, and varying weather conditions. It’s typically calculated using PVsyst, a tool that incorporates more parameters for an accurate assessment of annual production.


Methodology for Calculating Bifacial Gain


  1. Weather Data Acquisition

Reliable weather data with albedo values is the foundation for calculating bifacial gain. In the U.S., common sources include:


The choice of provider depends on customer preferences, but differences between these data sets are minimal (often within a few percentage points).


  1. Simulation with SAM

The first step when using SAM is to input the weather file into SAM to calculate the system's maximum short circuit current (ISC). Then divide the calculated ISC by the nominal ISC from the panel's datasheet to derive bifacial gain. For example, if the value is 1.2, the bifacial gain is 20% under ideal conditions. 

Note that while maximum bifacial gain is used for conservative wire sizing and system design, it doesn’t reflect annual energy yield.


  1. Refining Results with PVsyst

The next step is using PVsyst to integrate additional loss factors, such as:

  • Structural Shading

  • Shedding Transparency

  • Racking System Impact


These parameters are vendor-specific, and values vary widely. For example, Manufacturer A might have a 5% structural shading loss, while Manufacturer B’s is 10%. Carefully selecting racking systems with optimal parameters ensures higher efficiency.


PVsyst is valuable because its results accurately predict real-time annual production, enabling more realistic expectations of bifacial gain.


The Reality of Bifacial Gain

Many assume that a bifacial gain of 25% equates to 25% additional production. However, real-world results are significantly lower due to the disparity between maximum power gain (from SAM) and average annual production (from PVsyst). For example, a system with a 25% maximum bifacial gain might achieve only 10% extra energy annually.


Using Bifacial Gain Data for Code Compliance and Efficiency

The National Electric Code (NEC) offers two approaches for incorporating bifacial gain into system design:


  1. Multiply the short circuit current by 1.25 for a conservative estimate.


  2. Use SAM to calculate gain for a more precise, albeit complex, result.


While the 1.25 multiplier is simpler, it can lead to overdesign or inefficiencies. The SAM-based approach, though more accurate, requires robust data and modeling expertise.


Optimizing Bifacial Solar System Performance


Accurate bifacial gain modeling ensures systems are designed to maximize energy production while meeting regulatory and operational standards. Tools like SAM and PVsyst, combined with high-quality weather data and trusted equipment, enable utility-scale solar firms to deliver reliable, high-performance projects tailored to customer needs.


Looking for support with your utility-scale solar system design and engineering?


Get in touch with an expert at Castillo Engineering to ensure your system is equipped to meet the highest standards of reliability and performance.

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