Introduction
Laboratory testing plays a critical role in validating photovoltaic (PV) module quality, but controlled indoor conditions cannot always replicate the complexities of real-world operation. Solar modules installed in the field are continuously exposed to sunlight, temperature fluctuations, humidity, wind, and other environmental stressors that may trigger degradation mechanisms not visible during accelerated laboratory testing.
This is where the IEC 61215-2:2021 MQT 08 Outdoor Exposure Test becomes essential. The test is designed to evaluate a module’s ability to withstand actual outdoor operating conditions and identify synergistic degradation effects that may not emerge during indoor qualification sequences.
For manufacturers, EPCs, investors, and project developers, understanding the purpose and methodology of MQT 08 is important for assessing long-term PV module reliability and minimizing technical risk in solar projects.
What Is the IEC 61215-2 MQT 08 Outdoor Exposure Test?
The Outdoor Exposure Test (MQT 08) is part of the IEC 61215 qualification sequence for terrestrial PV modules. Its primary objective is to expose solar modules to real outdoor environmental conditions over a defined irradiation period.
Unlike accelerated stress tests performed in environmental chambers, MQT 08 places the module in actual field conditions to reveal:
• Potential synergistic degradation effects
• Early signs of material incompatibility
• Environmental stress interactions
• Field-related reliability concerns
• Hidden weaknesses not detectable in laboratory-only testing
The test acts as a bridge between controlled qualification procedures and real-world deployment conditions.
Purpose of the Outdoor Exposure Test
According to IEC 61215-2:2021, the purpose of MQT 08 is:
“To make a preliminary assessment of the ability of the module to withstand exposure to outdoor conditions and to reveal any synergistic degradation effects which may not be detected by laboratory tests.”
In practical terms, this means the test helps determine whether a module can maintain structural and electrical integrity when subjected to prolonged natural sunlight and environmental exposure.
Outdoor testing is especially important because some degradation mechanisms only appear when multiple stress factors occur simultaneously, including:
• UV radiation
• Thermal cycling from day/night temperature changes
• Humidity exposure
• Mechanical stress
• Electrical loading during operation
Key Apparatus Requirements for MQT 08
IEC 61215-2 specifies several important setup requirements to ensure test consistency and reliability.
1. Open Rack Mounting Structure
The module must be mounted on an open rack designed to:
• Minimize heat conduction
• Allow free airflow
• Reduce thermal interference
• Simulate realistic field installation conditions
For modules not intended for open-rack installation, mounting must follow manufacturer recommendations.
2. Solar Irradiation Monitor
An irradiation monitor with an accuracy of ±5% must be installed:
• In the same plane as the test modules
• Within 0.3 meters of the test array
This ensures accurate measurement of cumulative solar exposure throughout the test duration.
3. Proper Module Mounting
Modules must be mounted:
• Co-planar with the irradiation monitor
• Using manufacturer-recommended methods
Correct installation geometry is critical for obtaining reliable exposure data.
4. Resistive Load or MPPT Device
The module must operate near its maximum power point using either:
• A resistive load, or
• An electronic Maximum Power Point Tracker (MPPT)
This requirement simulates real operating conditions during outdoor exposure.
MQT 08 Test Procedure Explained
The IEC standard outlines a structured procedure for conducting the outdoor exposure test.
Module Tilt Angle
The test module must be positioned:
(1) Normal to the local latitude ±5°
(2) With tilt angle documented in the test report
This orientation ensures representative solar exposure conditions.
Outdoor Operational Exposure
The module is mounted outdoors while connected to:
• A resistive load, or
• An electronic MPPT system
Additionally:
• Hot-spot protective devices recommended by the manufacturer must be installed before testing.
Required Irradiation Level
The module must be exposed to a cumulative solar irradiation of at least:
60 kWh/m²
This exposure threshold ensures the module experiences meaningful environmental stress.
Cleaning During Testing
The standard allows modules to be cleaned during or after testing according to manufacturer instructions.
This is important because excessive dirt accumulation could artificially affect performance measurements.
Final Measurements After Outdoor Exposure
After completing the irradiation exposure, the module undergoes additional qualification measurements.
The IEC standard requires repeating:
• MQT 01 (Visual Inspection)
• MQT 15 (Wet Leakage Current Test)
These post-exposure evaluations verify whether outdoor conditions caused visible defects or compromised electrical insulation integrity.
Pass/Fail Criteria for MQT 08
To successfully pass the Outdoor Exposure Test, the module must meet the following requirements:
No Major Visual Defects
The module must show no evidence of major visual defects as defined in IEC 61215-1.
Examples include:
• Delamination
• Glass breakage
• Corrosion
• Backsheet cracking
• Severe discoloration
• Cell damage
Wet Leakage Current Compliance
The module must continue meeting the same wet leakage current requirements as the initial measurements.
This confirms that electrical insulation performance remains intact after outdoor exposure.
Why MQT 08 Matters for PV Module Quality Assurance
Although MQT 08 is considered a preliminary outdoor assessment rather than a long-term field reliability study, it still provides valuable insights into module durability.
Identifying Hidden Reliability Risks
Some degradation modes only occur when environmental stresses interact simultaneously.
Outdoor exposure testing can reveal:
• Encapsulant degradation
• UV-induced discoloration
• Junction box weaknesses
• Moisture ingress pathways
• Thermal mismatch issues
Supporting Bankability Assessments
Investors and lenders increasingly scrutinize module reliability data before financing utility-scale solar projects.
Successful completion of MQT 08 helps support:
• Product qualification
• Technical due diligence
• Supplier evaluation
• Long-term energy yield confidence
Improving Manufacturing Quality
Manufacturers can use outdoor exposure data to improve:
• Material selection
• Bill of materials (BOM) validation
• Process optimization
• Product durability
Outdoor Exposure Testing vs Accelerated Aging Tests
It is important to understand that MQT 08 complements—not replaces—accelerated aging tests such as:
• Damp Heat (MQT 13)
• Thermal Cycling (MQT 11)
• Humidity Freeze (MQT 12)
• UV Preconditioning (MQT 10)
Accelerated tests simulate years of stress within laboratory chambers, while outdoor exposure evaluates actual environmental interaction under natural conditions.
Both approaches are necessary for comprehensive PV reliability assessment.
The Growing Importance of Independent PV Testing
As the solar industry continues scaling globally, independent testing and verification are becoming increasingly important.
Developers and asset owners are placing greater emphasis on:
• Module quality assurance
• Third-party laboratory testing
• Factory audits
• Supply chain traceability
• Technical risk mitigation
Outdoor exposure testing remains one important component within a broader PV quality assurance strategy.
Conclusion
The IEC 61215-2 MQT 08 Outdoor Exposure Test provides valuable insight into how PV modules perform under real-world environmental conditions. By exposing modules to natural sunlight, operational electrical loading, and outdoor climate variations, the test helps identify degradation mechanisms that may not appear during laboratory-only qualification testing.
For manufacturers, project developers, investors, and asset owners, understanding MQT 08 is essential for evaluating long-term module reliability and reducing technical risk across solar projects.
As PV systems are expected to operate reliably for 25 years or more, robust testing standards like IEC 61215 remain critical for ensuring durable, bankable, and high-performing solar assets.
Looking to validate your PV modules or strengthen your quality assurance process? Contact Sinovoltaics today to learn how our independent testing, inspection, and technical advisory services can support your solar projects and safeguard your investments. Explore our PV laboratory testing advisory services.
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