Researchers from the Technical University of Denmark have developed a novel method for detecting low-energy front glass cracks in PV modules using daylight electroluminescence (EL) imaging. Low-energy fractures are cracks that initially produce localized damage without significant propagation but have the potential to expand over time. Because they are subtle, they often go unnoticed in large-scale inspections.
“The novelty of this work is that we show that low-energy glass cracks in PV modules can be consistently detected using daylight electroluminescence (EL) imaging acquired in motion,” corresponding author Rodrigo del Prado Santamaría told pv magazine. “Traditionally, EL imaging is used to identify material defects in the solar cells themselves, while glass crack detection relies on visual inspections or infrared imaging. Our research shows that a single daylight EL inspection can provide information on both internal cell defects and glass cracks, which could make inspections more efficient and informative.”
Del Prado Santamaría added that the method enables the detection of cracks that are not visible in conventional RGB images or infrared thermography. “Furthermore, sunlight and camera motion, which are normally considered challenges in EL imaging, actually become part of the solution. During daylight drone EL inspections, small movements between frames create subtle changes in how sunlight reflects from cracked glass surfaces. When the images are reconstructed, those variations make the cracks stand out much more clearly,” he explained.
The method first forward-biases the PV module with a modulated current, causing it to emit an EL signal. An InGaAs short-wave infrared (SWIR) camera then records multiple daylight images while the camera is in slight motion. This movement causes cracked glass to reflect sunlight differently from frame to frame. Software then detects module corners, tracks and aligns the module across all frames, and applies fast Fourier transform (FFT) processing to extract the EL signal while reducing daylight noise. The reconstructed image reveals both conventional EL information, such as cell defects, and glass cracks, which become visible due to changing daylight reflections.
The researchers evaluated the method in two ways. First, they conducted controlled laboratory-style daylight experiments using a 305 W glass-glass PV module with a pre-existing glass crack. Slight camera motion was manually introduced to simulate drone movement, while varying motion levels, imaging distances, and illumination conditions. Second, they validated the technique during a real drone inspection at the university’s PV plant, using a commercial drone equipped with an InGaAs camera to inspect operating PV modules under daylight conditions and compare results with conventional RGB imaging and infrared thermography.
The team said the results confirm the viability of the proposed approach. They also systematically evaluated its performance and limitations, finding that with a 640 × 512-pixel InGaAs camera, the optimal imaging distance was 8–12 m, while crack detection reliability decreased at distances beyond 15 m.
“We are currently exploring several directions for follow-up research,” concluded Del Prado Santamaría. “One question we would like to investigate is whether the same crack-detection mechanism can be achieved using short-wave infrared (SWIR) imaging without the need for electrical modulation. Our results suggest that crack visibility is strongly linked to sunlight reflections and motion, so there may be alternative ways of exploiting the same effect. We are also interested in understanding how factors such as solar irradiance, viewing angle, and camera characteristics influence crack visibility. Ultimately, the goal is to develop drone-based inspection systems that can identify multiple types of defects simultaneously and improve the reliability and safety of large PV plants.”
The method was presented in “A novel method for detecting low-energy front glass cracks in photovoltaic modules using daylight electroluminescence imaging,” published in Solar Energy.
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