Solar Panel Degradation Testing Guide (2026)
Degradation testing measures how a photovoltaic (PV) module loses power over time and under stress. Every module degrades; what matters is how much, how fast, and whether the loss is reversible. This guide explains the main degradation mechanisms, how IEC 61215 addresses them, and which instruments support each measurement stage.
The main degradation mechanisms
| Mechanism | What happens | How it is tested |
|---|---|---|
| LID (Light-Induced Degradation) | Power loss in the first hours of light exposure, mainly in p-type c-Si cells | Controlled light soaking with I-V tracking |
| LeTID (Light and elevated Temperature Induced Degradation) | Slower, temperature-accelerated loss | Light + heat exposure with periodic I-V |
| PID (Potential-Induced Degradation) | Loss driven by high system voltage and humidity | Voltage bias + damp conditions |
| Hot-spot degradation | Localized overheating from partial shading or defects | Thermal imaging + I-V |
The common requirement across all of these: repeated, accurate I-V measurement before, during, and after stress, to quantify how much power was lost.
How IEC 61215 addresses degradation
- UV preconditioning: exposure before other tests to trigger initial degradation.
- Light-induced degradation test: measures the power loss after initial light exposure.
- Thermal cycling / damp heat / humidity freeze: environmental stress followed by I-V re-test.
- Stabilization: the 2021 edition clarifies how to measure "stabilized" performance so degradation is not confused with measurement variation.
A module passes qualification only if its power remains above defined thresholds after each step. Degradation testing is therefore central to proving long-term reliability.
Which TDM instruments support degradation testing
- SE910 Light Degradation Tester: performs light degradation testing with controlled illumination; product data references IEC 61215 and IEC 61730.
- SE920 Steady-state IV & Degradation Tester: an A+A+A+ solar simulator (300-1200 nm, 200-1200 W/m²) for steady-state I-V characterization and degradation tracking. This is the workhorse for repeated I-V re-tests.
- SE400 PVK MPPT Testing System: an A+A+A+ LED MPPT tester (IEC 60904-9, 0.2-1.2 SUN) for maximum-power-point stability evaluation during degradation studies.
- SE68 EPL/AOI/Degradation Integration: combines EPL mapping, AOI and 1-sun spectral degradation on 310x310 mm samples.
Important: A product page referencing IEC 61215 or IEC 61730 does not by itself establish equipment certification or complete test-sequence coverage. Qualification must run under a proper laboratory framework; these instruments support the measurement steps described.
A practical note on LID vs LeTID
LID and LeTID are often confused. LID appears within the first days of light exposure and is largely recoverable; LeTID develops over weeks under light plus heat and can be more severe. A proper degradation program measures power at multiple intervals to separate the two, which is why steady-state I-V tracking is essential.
Frequently asked questions
What is the difference between LID and LeTID?
LID is rapid, early, largely recoverable light-induced loss; LeTID is slower, temperature-accelerated loss that develops over weeks. They require different measurement intervals.
Does IEC 61215 include degradation testing?
Yes. UV preconditioning, the light-induced degradation test, and post-stress I-V re-tests all quantify degradation. Safety is covered separately by IEC 61730.
How is degradation quantified?
By measuring I-V characteristics before, during, and after stress, then comparing maximum power (Pmax) against the initial value.
Related guides and products
- IEC 61215: Solar Module Performance Testing Guide
- I-V Curve Testing Guide
- PV Module Testing solutions
- SE910 Light Degradation Tester
- SE920 Steady-state IV & Degradation
