Tests & methodology

The 2025 edition of the PV Module Index Report compiles the results of bankability and beyond-qualification tests conducted at RETC’s accredited laboratories over 12 months, spanning Q2 2024 through Q1 2025. Like previous editions, this year’s report catalogs testing sequences and data according to three interrelated and equally influential manufacturing disciplines: module quality, performance, and reliability.

We present performance distribution data for specific test sequences within each of these three disciplines. By filtering these comparative data, project stakeholders can specify products or qualify project designs best suited to a specific environment, location, asset, or portfolio.

To characterize long-term in-field reliability, industry stakeholders—including subject matter experts at RETC—have developed enhanced testing standards, procedures, and sequences that go beyond minimum product safety and design qualification requirements. These beyond-qualification test protocols put additional stress on modules to identify areas of weakness and better predict long-term in-field reliability.
As solar projects increase in scale, frequency, and geographical distribution, project stakeholders must remain vigilant regarding performance risks. How do different technologies perform under low-irradiance conditions or in relation to changing sun angles? Is a specific bill of materials susceptible to irradiance- or temperature-induced degradation under expected conditions of use? Will modules and systems perform as expected under the peak power conditions critical to energy yield optimization? Laboratory data allow for a science- and engineering-based understanding of both short- and long-term PV system performance.
To meet user standards, PV modules must be durable enough to withstand multiple decades of in-field exposure. Not surprisingly, reliable in-field operation over a 25-30 year service life is not an accident. Studies have consistently shown a strong positive correlation between quality and return on investment and other profitability indicators.

Award Summary

Overall Highest Achiever

To achieve RETC’s top honor, module companies must our high achievement criteria in three disciplines: module reliability, performance, and quality.

In other words, “Overall Highest Achiever” status effectively indicates that RETC recognizes a company for “High Achievement in Reliability,” “High Achievement in Performance,” and “High Achievement in Quality.”

High Achievement in Discipline

To achieve discipline-level recognition, such as “High Achievement in Performance,” module companies must excel across multiple test sequences within the module performance or reliability disciplines.

RETC awards discipline-level recognition to manufacturers that do not meet our “Overall Highest Achiever” criteria.

Test Category High Achiever

To achieve test category-level recognition, module companies must meet high achievement criteria within at least one individual test sequence.

RETC awards “Test Category High Achiever” recognition to manufacturers that do not meet our criteria for discipline-level or overall high achievement.

Performance Indicators

CEC Certification

Solar modules must be included on an eligible equipment list maintained and regularly updated by the CEC to qualify for solar incentive programs around the US. This CEC listing requires additional testing and characterization beyond the basic UL product certification tests.
Conversion Efficiency

The percentage of incident solar energy converted to electrical energy is an essential figure of merit for PV modules and cell technologies. Nominal module conversion efficiency is determined by dividing a product’s nameplate STC-rated power by its total aperture area. Cell technology and module design play a significant role in module efficiency.
Incidence Angle Modifier (IAM)

Performance characteristic that accounts for changes in PV module output based on changing sun angles. Essential for understanding module performance at different times or seasons, especially early or late in the day or in winter when the sun is low on the horizon.
Light & Elevated Temperature Induced Degradation (LeTID)

Newer cell technologies may experience a type of long-term in-field degradation associated with exposure to light and elevated temperatures. Used to characterize LeTID susceptibility.
Light Induced Degradation (LID)

Testing to IEC standards to ensure manufacturing quality control and in-field reliability. LID is a type of degradation resulting from exposure to sunlight that impacts some PV cell types but not others.
PAN Files

The de facto standard module characterization file format is a PAN file, which defines 22 parameters that PVsyst software uses for its production modeling calculations.

Reliability Indicators

Damp Heat

Aims to characterize a PV module’s ability to withstand prolonged exposure to humid, high-temperature environments. Takes place inside an environmental chamber.
Dynamic Mechanical Load (DML)

Evaluates a module’s ability to withstand wind loading. Whereas standard mechanical load (ML) tests simulate static snow and ice loads, DML testing simulates the dynamic push-pull loads associated with hurricanes, typhoons and other high-wind events.
Humidity Freeze (HF)

Characterizes a PV module’s ability to withstand the alternating effects of high heat and humidity followed by extreme cold. For this accelerated aging test, modules in an environmental chambe
Potential Induced Degradation (PID)

The PID test protocol places rack-mounted modules in an environmental chamber, which controls temperature and humidity, and exposes them to a voltage bias of several hundred volts with respect to the mounting structure.
Thermal Cycling (TC)

Calls for extended 600-cycle TC600 testing as a means of detecting weaknesses in module designs. TC testing assesses product reliability and identifies thermal fatigue failure modes.
Ultraviolet (UV) Exposure

The enhanced UV preconditioning test conducted for accelerated reliability assessment exposes modules to two cycles of UV irradiation at 45 kWh/m2, which is six times greater than the IEC 61215 requirements for product qualification.