A German research group has developed a novel, nondestructive method to quantify water ingress in solar modules on site. The technique uses near-infrared absorption (NIRA) spectroscopy calibrated against absolute water content measured via Karl–Fischer titration (KFT), enabling inspectors to determine moisture levels inside modules without opening them.
“The methodology is noninvasive, requires no bill-of-material modifications such as additional sensors, and is broadly applicable to field-deployed modules, provided prior calibration has been conducted,” corresponding author Anton Mordvinkin told pv magazine. “Unlike conventional approaches, it does not rely on assumptions such as Henry’s law or on approximations of evolving barrier properties or uncertainties related to a module’s internal microclimate.”
Mordvinkin said the approach lays the groundwork for more precise modeling of moisture ingress and improves the reliability of module lifetime predictions. “It provides actionable insights for manufacturers to optimize the design and qualification of products resistant to moisture-induced degradation mechanisms, including moisture-induced degradation (MID) and potential-induced degradation (PID), particularly in challenging environments such as floating PV systems and tropical climates, as well as for emerging technologies like tandem cells,” he added.
He also noted that the method enhances solar park inspection by enabling the identification of modules with insulation deficiencies, supporting targeted mitigation measures. “These advances contribute directly to improved asset bankability and provide a robust technical basis for future warranty and reclamation processes,” he said.
Image: Fraunhofer Center for Silicon Photovoltaics (CSP), Progress in Photovoltaics: Research and Applications, CC BY 4.0
The novel method involves exposing polymer materials commonly used in PV modules to varying moisture levels through damp-heat testing. Each sample is then measured using near-infrared absorption (NIRA) spectroscopy, in which water is detected by its strong absorption of infrared light. However, as NIRA provides only a relative signal, the same samples are subsequently analyzed using Karl–Fischer titration (KFT), a technique that heats the material and precisely quantifies the amount of water released. By correlating the NIRA signal with the absolute water content determined by KFT, the researchers establish calibration curves for each material.
The materials tested include encapsulants such as ethylene-vinyl acetate (EVA), polyolefin elastomer (POE), thermoplastic polyolefin (TPO), and thermoplastic polyurethane (TPU), as well as backsheets such as polyethylene terephthalate (PET), polypropylene (PP), polyamide-aluminum-polyamide (AAA), polyvinylidene fluoride (PVDF), and fluorinated-coated PET.
Image: Fraunhofer Center for Silicon Photovoltaics (CSP), Progress in Photovoltaics: Research and Applications, CC BY 4.0
Once calibrated, a handheld NIRA spectroscopy device can be used directly on installed the modules. To demonstrate this capability, the research team tested minimodules with PET- and PP-based backsheets under damp-heat conditions, polymer coupons exposed to accelerated ultraviolet (UV) radiation and humidity aging, rooftop modules exhibiting backsheet cracking and snail trails, and field-retrieved modules with both cracked and intact AAA backsheets to compare real-world moisture ingress and degradation behavior.
The tests showed that PET-based modules absorbed more water than PP-based modules. In field studies, modules with backsheet and cell cracking exhibited up to 50% higher water content, while modules with cracked AAA backsheets absorbed water up to ten times faster than intact reference modules.
“In this work, it was found that the improved barrier performance of PP is primarily governed by its lower water solubility, whereas the diffusion coefficients of both materials are comparable,” said Mordvinkin. “This provides a more detailed mechanistic explanation for the previously observed differences and is consistent with trends reported in the literature.”
“Another particularly insightful observation is the presence of a non-homogeneous water-content distribution in modules with severely degraded backsheets after extended outdoor exposure of over 7 years,” he added. “Localized moisture accumulation was significantly enhanced in regions with cell microcracks, which correlate with visually observable snail trail patterns. This finding points to a coupling between mechanical degradation and localized moisture ingress behavior.”
The new method was presented in “Nondestructive Quantification of Water Ingress in PV Modules via Spectroscopic and Chemical Analysis for Enhanced Quality Assurance and On-Site Inspection,” published in Progress in Photovoltaics: Research and Applications. Researchers from Germany’s Fraunhofer Center for Silicon Photovoltaics (CSP), Fraunhofer Institute for Microstructure and Systems (IMWS), and Forschungszentrum Jülich have contributed to the study.
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