Photovoltaic (PV) modules rarely operate under perfect sunlight conditions throughout their lifetime. Cloud cover, early morning and late afternoon conditions, shading, and seasonal variations can all reduce irradiance levels in real-world environments. To evaluate module behavior under these conditions, IEC 61215-2:2021 includes the MQT 07 test: Performance at Low Irradiance.
This test helps determine how the electrical performance of a PV module varies when operating at lower irradiance levels while maintaining controlled temperature conditions.
What is MQT 07 in IEC 61215-2:2021?
MQT 07 is designed to measure the electrical performance of PV modules at:
• Irradiance: 200 W/m²
• Module temperature: 25°C
The test evaluates the module’s current-voltage (I-V) characteristics under low-light conditions to assess how effectively the module performs when irradiance levels are significantly below Standard Test Conditions (STC).
Because many PV systems spend a considerable amount of operating time under partial sunlight, low irradiance performance is an important factor in overall energy yield assessments.
Purpose of MQT 07 Testing
The purpose of MQT 07 is to determine how the electrical characteristics of the PV module vary with load at low irradiance levels.
This testing helps manufacturers, project developers, and investors:
• Evaluate low-light energy production performance
• Compare module technologies under reduced irradiance
• Verify module stability under non-STC conditions
• Assess bifacial and advanced module behavior in low-light environments
Low irradiance performance testing can provide valuable insights into real-world module operation and long-term energy generation potential.
Low irradiance performance testing can provide valuable insights into real-world module operation and long-term energy generation potential. This test is particularly crucial in environments with lower irradiance conditions, where module performance under reduced sunlight can significantly impact overall energy yield.
Apparatus Requirements for MQT 07
IEC 61215-2:2021 specifies that the testing apparatus for MQT 07 shall include the same setup used for MQT 02, along with additional capabilities required for low irradiance testing.
Irradiance Control Capability
The equipment must be capable of reducing irradiance to 200 W/m² without affecting:
• Relative spectral irradiance distribution
• Spatial uniformity
This requirement follows IEC 60904-10 guidance to ensure accurate and repeatable low-light measurements.
Temperature Monitoring
The apparatus must include a means for monitoring the temperature of:
• The test specimen
• The reference device
The required performance specifications are:
• Accuracy: ±1°C
• Repeatability: ±0.5°C
Requirements for Bifacial Modules
For bifacial PV modules, additional equipment is necessary, including:
• Baffles arranged around module edges
• A non-reflective cover for temporarily blocking irradiance
This setup allows separate evaluation of front-side and rear-side module performance under low irradiance conditions.
Requirements for Multi-Junction Modules
For multi-junction modules, the simulator and reference device must comply with the additional requirements specified in IEC TS 60904-1-1.
MQT 07 Testing Procedure
The testing procedure for MQT 07 follows controlled laboratory conditions to accurately characterize module performance at reduced irradiance.
1. Measure the I-V Characteristics
The current-voltage characteristic of the module is measured at:
• Temperature: 25 ± 2°C
• Irradiance: 200 ± 20 W/m²
Measurements are conducted in accordance with IEC 60904-1 using the apparatus described in Section 4.7.2.
2. Reduce Irradiance Without Spectral Distortion
The irradiance level shall be reduced using methods that do not affect the spectral irradiance distribution.
IEC 61215-2:2021 references techniques such as:
• Neutral density filters
• Alternative irradiance reduction methods compliant with IEC 60904-10
Maintaining spectral consistency is critical for obtaining meaningful low irradiance performance data.
3. Apply Temperature Corrections
If necessary, the module temperature shall be corrected to 25°C using:
• Temperature coefficients
• IEC 60904 series
• IEC 60891 correction methods
These corrections improve consistency between different testing environments and laboratories.
Special Requirements for Flexible and Very Large Modules
Flexible Modules
Flexible PV modules must be tested while fully unfolded and positioned flat during maximum power determination.
Very Large Modules
Very large modules, as defined in IEC 61215-1:2021, may be tested at the manufacturer’s facility provided all testing requirements remain compliant with the standard.
Additional Procedure for Bifacial Modules
IEC 61215-2:2021 includes specific procedures for bifacial module evaluation at low irradiance.
Two single-sided measurements must be performed at 200 W/m²:
• One measurement on the front side
• One measurement on the rear side
The testing setup uses:
• Baffles
• Back-cover screening
The bifaciality coefficients at low irradiance are then calculated according to IEC TS 60904-1-2, except using 200 W/m² instead of 1000 W/m².
Multi-Junction Module Considerations
For multi-junction PV modules, measurements shall proceed according to IEC TS 60904-1-1 requirements.
These additional procedures help ensure accurate characterization of advanced PV technologies with more complex spectral responses.
Why Low Irradiance Testing Matters
Low irradiance performance has become increasingly important as PV systems are deployed across diverse climates and environmental conditions.
Modules with strong low-light behavior may achieve:
• Improved early morning and late afternoon production
• Better energy yield during cloudy conditions
• Enhanced annual energy generation
• More predictable field performance
As the industry continues to adopt bifacial and high-efficiency technologies, low irradiance testing provides valuable performance insights beyond standard STC measurements.
Conclusion
IEC 61215-2:2021 MQT 07 establishes a standardized method for evaluating PV module performance under low irradiance conditions. By carefully controlling irradiance reduction, spectral distribution, temperature, and measurement accuracy, the test enables reliable comparison of module behavior in reduced sunlight environments.
The test is especially important for assessing modern PV technologies such as bifacial and multi-junction modules, where low-light performance can significantly influence real-world energy yield.
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 help safeguard your investments. You can also explore our PV Lab Test Advisor to identify the most suitable testing approach for your PV modules and project requirements.