Introduction
Solar modules spend decades exposed to sunlight, enduring continuous ultraviolet (UV) radiation throughout their operational lifetime. While photovoltaic cells generate electricity from sunlight, prolonged UV exposure can gradually degrade encapsulants, backsheets, adhesives, coatings, and other polymeric materials within the module. If these materials deteriorate prematurely, module performance, reliability, and safety can be compromised.
To evaluate a module's resistance to UV-related degradation, the International Electrotechnical Commission (IEC) includes the UV Preconditioning Test (MQT 10) within the IEC 61215-2:2021 qualification sequence. The test subjects photovoltaic modules to controlled UV irradiation before subsequent environmental stress tests, helping identify weaknesses in materials and adhesive bonds that may not be apparent during standard electrical testing.
This article explains the purpose, test methodology, equipment requirements, acceptance criteria, and importance of the IEC 61215 MQT 10 UV Preconditioning Test.
What Is the IEC 61215 MQT 10 UV Preconditioning Test?
The UV Preconditioning Test is designed to expose PV modules to elevated levels of ultraviolet radiation before thermal and moisture-related stress testing.
According to IEC 61215-2:2021 Section 4.10.1, the purpose of MQT 10 is:
"To precondition the module with ultraviolet (UV) radiation before thermal cycle and humidity freeze tests to identify materials and adhesive bonds that are susceptible to UV degradation."
The test acts as an accelerated screening method to reveal vulnerabilities in module materials that could develop over years of outdoor exposure.
It is important to note that MQT 10 is not intended to reproduce the complete lifetime UV exposure of a solar module. Instead, it serves as a comparative qualification test to identify modules with poor UV durability before they enter the market.
Why UV Resistance Matters in Solar Modules
A PV module contains numerous non-cell components that can be affected by ultraviolet (UV) radiation. Prolonged UV exposure can degrade encapsulants, backsheets, adhesives, junction boxes, and other polymer-based materials, potentially affecting module reliability and long-term performance.
As the market increasingly adopts TOPCon bifacial modules, evaluating UV resistance has become even more important. Research has shown that TOPCon technology may be more susceptible to ultraviolet-induced degradation (UVID) than some conventional cell technologies, making UV durability testing a key consideration when assessing long-term module reliability.
These include:
• Encapsulants (EVA, POE, and alternatives)
• Backsheets
• Edge seals
• Junction box adhesives
• Cell interconnection insulation
• Front-sheet coatings
• Frame sealants
Over time, UV-induced degradation can cause:
Material Discoloration
Yellowing or browning of encapsulants may reduce light transmission and lower energy production.
Delamination
UV exposure can weaken adhesive bonds between module layers, leading to moisture ingress and accelerated degradation.
Cracking and Brittleness
Polymeric materials may become brittle after prolonged UV exposure, increasing susceptibility to mechanical failure.
Reduced Reliability
UV-related degradation often accelerates the effects of temperature cycling, humidity, and environmental stress.
The MQT 10 test helps identify these risks during product qualification.
Equipment Required for MQT 10 Testing
IEC 61215-2:2021 specifies several key equipment requirements.
Temperature-Controlled Test Chamber
The chamber must:
• Accommodate the module and UV light source
• Maintain module temperature at:
60 ± 5°C
This elevated temperature accelerates material aging while remaining representative of field conditions.
Temperature Monitoring System
Temperature sensors must provide:
• Accuracy of ±2.0°C
• Repeatability of ±0.5°C
Sensors are attached to the front or rear surface near the module center without blocking UV irradiation on active cells.
UV Irradiance Measurement Equipment
Instrumentation must measure UV irradiance in two wavelength bands:
• 280 nm to 320 nm
• 320 nm to 400 nm
Measurement uncertainty must be:
±15% or better
UV Light Source
The UV source must:
• Provide irradiance uniformity within ±15% across the test plane
• Produce negligible irradiance below 280 nm
• Deliver the total UV dosage required by the standard
The spectral distribution is carefully controlled to simulate UV exposure relevant to photovoltaic applications.
Module Electrical Configuration
During exposure, the module must be either:
• Short-circuited, or
• Open-circuited
The configuration follows manufacturer recommendations and must be documented in the test report.
IEC 61215 MQT 10 Test Procedure
Step 1: Verify UV Irradiance Conditions
Before testing begins, irradiance is measured at the module test plane.
IEC requires:
Wavelength Range
280 nm to 400 nm
Maximum Irradiance
250 W/m²
This level is approximately five times greater than natural UV sunlight intensity.
Uniformity
The irradiance distribution across the test plane must remain within:
±15%
Step 2: Install the Module
The module is mounted in the test chamber according to manufacturer instructions.
Requirements include:
• Correct module positioning relative to the UV source
• Proper support structures
• Appropriate mounting methods for flexible modules
• Temperature sensor installation
Module temperature is stabilized at:
60 ± 5°C
Step 3: Apply UV Exposure
The front side of the module is exposed to ultraviolet radiation.
IEC specifies a minimum accumulated UV dose of:
15 kWh/m²
within the wavelength range:
280 nm to 400 nm
Additionally:
• At least 3%
• But not more than 10%
of total UV energy must fall within:
280 nm to 320 nm
This requirement ensures realistic UV spectral exposure.
Step 4: Bifacial Module Testing
For bifacial PV modules, the procedure must be repeated on the rear side of the module.
Because bifacial modules receive sunlight from both sides during operation, both surfaces require UV durability verification.
What Happens After UV Preconditioning?
MQT 10 is a preconditioning test rather than a standalone durability assessment.
Following UV exposure, the module proceeds to additional qualification tests, including:
Thermal Cycling
Repeated temperature changes evaluate material fatigue and interconnection reliability.
Humidity Freeze Testing
Alternating humidity and freezing conditions assess moisture-related degradation. The UV exposure helps accelerate degradation mechanisms that may otherwise remain hidden during these subsequent tests.
Pass/Fail Criteria
Following UV preconditioning, the standard requires:
Repeat Measurements
The module must successfully complete:
• MQT 01 – Visual Inspection
• MQT 15 – Wet Leakage Current Test
Visual Inspection Requirements
No major visual defects are permitted, including:
• Delamination
• Cracks
• Severe discoloration
• Structural damage
Visual criteria follow IEC 61215-1:2021 requirements.
Wet Leakage Current Requirements
The module must satisfy the same wet leakage current requirements established during initial qualification testing.
Failure to meet these requirements indicates that UV exposure may have compromised insulation integrity or module construction.
Common Failure Mechanisms Revealed by MQT 10
The UV Preconditioning Test frequently identifies weaknesses in:
Encapsulant Formulations
Poor UV stability can cause:
• Yellowing
• Browning
• Reduced optical transmission
Adhesive Systems
UV exposure may weaken bonds between:
• Glass and encapsulant
• Encapsulant and backsheet
• Junction box and backsheet
Polymeric Backsheets
Extended UV exposure can result in:
• Cracking
• Chalk formation|
• Surface degradation
Edge Seal Materials
Degraded edge seals increase the risk of moisture ingress and corrosion during field operation.
Why MQT 10 Matters for Solar Investors and Developers
Although UV preconditioning is only one part of IEC qualification, it provides valuable insight into long-term module reliability.
For developers, EPCs, investors, and asset owners, UV durability influences:
- Performance retention
- Maintenance costs
- Warranty risk
- Project bankability
- Long-term energy yield
Modules that pass MQT 10 demonstrate improved resistance to environmental aging and material degradation.
However, IEC certification alone should not be considered a complete assessment of module quality. Independent manufacturing audits, bill of materials reviews, and reliability assessments remain critical components of supplier due diligence.
Best Practices Beyond IEC Compliance
To further reduce UV-related risks:
• Review manufacturer bill of materials consistency.
• Verify encapsulant and backsheet supplier qualifications.
• Examine independent laboratory reliability reports.
• Assess field performance history.
• Conduct factory quality audits.
• Evaluate long-term degradation data.
These measures provide a more complete understanding of module durability than certification alone.
Conclusion
The IEC 61215 MQT 10 UV Preconditioning Test plays a critical role in evaluating the durability of solar module materials exposed to ultraviolet radiation. By exposing modules to controlled UV energy before environmental stress testing, the procedure helps identify weaknesses in encapsulants, adhesives, backsheets, and other critical components that may impact long-term reliability.
As module lifetimes continue to extend beyond 25 years, resistance to UV-induced degradation remains an essential factor in ensuring project performance and protecting investment returns. Understanding how manufacturers perform in tests such as MQT 10 helps developers, EPCs, investors, and asset owners make more informed procurement decisions.
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By combining IEC qualification results with independent quality assurance data, stakeholders can reduce risk and improve long-term project performance.
References
1. IEC 61215-2:2021 – Terrestrial Photovoltaic (PV) Modules – Design Qualification and Type Approval – Part 2: Test Procedures, Section 4.10 UV Preconditioning Test (MQT 10).
2. IEC 61215-1:2021 – Terrestrial Photovoltaic (PV) Modules – Design Qualification and Type Approval – Part 1: Test Requirements.
3. National Renewable Energy Laboratory (NREL), PV Module Reliability Research Program.
4. International Energy Agency Photovoltaic Power Systems Programme (IEA PVPS), PV Module Reliability Reports.