What Is Electroluminescence Testing?
Electroluminescence testing (EL test) is an imaging method that makes invisible defects in solar cells visible. Similar to an X-ray in medicine, the EL test reveals what is happening beneath the surface of a PV module – in particular:
- Microcracks in cells
- Cell breakage
- Contact defects
- Inactive areas
The test only works when an electrical current flows through the module – causing it to "glow" in the near-infrared range. This signal can be captured and analyzed with a specialized camera.
Why Is the EL Test So Important?
Many cell defects are not visible from the outside – neither to the naked eye nor through conventional performance measurements like the flash test. Especially with used PV modules or during repowering projects, the EL test is crucial for identifying hidden weak points.
In particular:
- Hail, transport, or installation errors cause microcracks that progressively worsen over time
- Modules may appear optically intact but already show significant cell damage internally
- Only with the EL test can a reliable statement be made about the actual condition of the cells
How Does the EL Test Work at 2nd Cycle?
- Power supply: The module is connected to a DC power source to energize the cells
- Darkroom: The test takes place in complete darkness, as the emitted light is extremely faint
- Infrared camera: A high-resolution camera captures the luminescence pattern of each cell
- AI-based analysis: The recorded image is automatically analyzed by our software – cracks, inactive zones, and defects are identified and classified
- Grading: Based on the EL result, the module receives a quality assessment that feeds into the overall reuse decision
What Can the EL Test Detect?
The EL test is particularly effective at detecting:
Microcracks and crack propagation in cells, cell fractures caused by mechanical loads, soldering and contact defects, and inactive or degraded cell areas.
- Microcracks and crack propagation in cells
- Cell fractures caused by mechanical loads
- Soldering and contact defects
These defects are often invisible in other tests but can significantly affect long-term performance and safety.
EL Testing as Part of Our Testing Line
The EL test at 2nd Cycle is not an isolated test – it is part of our fully automated, multi-stage testing process:
Visual inspection → Flash test → UV fluorescence → Electroluminescence → Wet leakage test
Only modules that pass all test stages receive the "Reuse" grading. The EL test plays a central role in this process as it reveals the deepest insights into cell quality.
At 2nd Cycle, we ensure that every module is thoroughly tested – because quality and safety are the foundation of sustainable reuse.
Conclusion
The electroluminescence test is one of the most important methods for assessing the true condition of a PV module. It makes defects visible that no other test can detect.