Prolonged exposure to heat and humidity is one of the most common causes of long-term degradation in solar panels. Moisture that slowly penetrates the module can corrode cell metallization, delaminate encapsulant, and degrade the insulation resistance, all without any visible sign until performance has already dropped significantly. The IEC 61215 MQT 13 damp heat test is designed to accelerate and expose exactly these failure mechanisms. Here is a complete breakdown of what the test involves.
What is the MQT 13 Damp Heat Test?
MQT 13, defined in IEC 61215-2:2021, is one of the most stringent environmental stress tests in the IEC 61215 qualification sequence. Its purpose is:
To determine the ability of the module to withstand the effects of long-term penetration of humidity.
Unlike the humidity-freeze test (MQT 12), which combines moisture with freezing temperatures, MQT 13 applies sustained high heat and humidity simultaneously over an extended period. The test is designed to evaluate the quality of the module's encapsulation, edge sealing, and the resistance of its internal materials to moisture-driven corrosion and degradation.
Required Apparatus
Requirements for the test chamber are listed in IEC 60068-2-78:2012. The chamber must be capable of maintaining the required temperature and relative humidity simultaneously over the full test duration.
Test Conditions and Procedure
The procedure for introducing the sample into the chamber and starting the test follows IEC 60068-2-78:2012. The test is carried out with the following conditions:
Test severities:
• Test temperature: (85 ± 2) °C
• Relative humidity: (85 ± 5) %
• Test duration: 1000 (+48/0) hours
No preconditioning shall be performed before placing the module in the chamber.
Module connectors shall be short-circuited, unless current is being applied according to options provided in some of the technology-specific parts.
For flexible modules, mount according to the manufacturer's documentation with prescribed substrate and adhesive or attachment/mounting means during the test.
Final Measurements
After completing the 1000-hour exposure, allow the module a recovery time of between 2 and 4 hours at (23 ± 5) °C and relative humidity less than 75%, under open-circuit conditions. Then repeat the following measurements:
• MQT 01 — Visual inspection
• MQT 15 — Wet leakage current test
Pass/Fail Criteria
A module passes MQT 13 if it meets both of the following requirements:
1. No evidence of major visual defects, as defined in IEC 61215-1:2021.
2. Wet leakage current must meet the same requirements as for the initial measurements.
Why MQT 13 Matters for PV Module Certification
The damp heat test is widely considered one of the toughest hurdles in the IEC 61215 sequence. One thousand hours at 85 °C and 85% relative humidity accelerates the equivalent of years of moisture exposure in humid field climates. Modules that fail typically show corrosion of cell busbars and fingers, delamination between the encapsulant and glass or backsheet, browning or yellowing of the encapsulant, and a drop in insulation resistance.
For project developers and buyers sourcing modules for humid tropical, coastal, or monsoon climates, MQT 13 performance is a particularly relevant indicator of long-term reliability. A module that passes this test demonstrates that its materials, edge sealing, and encapsulation quality are robust enough to resist moisture ingress under prolonged thermal stress, a critical factor in achieving the 25–30 year lifetimes that bankability depends on.
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Source: IEC 61215-2:2021 — Terrestrial photovoltaic (PV) modules – Design qualification and type approval – Part 2: Test procedures, Section 4.13