Photovoltaic (PV) modules are devices designed to transform sunlight into electricity. However, they can also work in the same way as a LED: By applying a polarization current, the solar module can be electrically stimulated to emit electroluminescence (EL) radiation. This phenomenon is particularly interesting because it allows you to acquire very detailed information about common failures on the modules using high-resolution imaging.
Something similar also happens if the module is stimulated with sunlight instead of electricity This phenomenon is called photoluminescence (PL). Both EL and PL are made up of very tiny signals in comparison to sunlight and so are difficult to measure.
Measuring the power that can be extracted from a module is a good way to evaluate its performance. However, it’s also important to look to the future and understand the performance capabilities of the PV plant as it ages. Therefore, the EL imaging technique is evolving year by year opening new opportunities for analysis and evaluation.
Visualizing failures
The visualization of failures is important in the evaluation of the manufacturing process, for contractual purposes, for a power loss forecast and for the bankability of a PV project.
Conventionally, the easiest way to use EL imaging was during the nighttime, due to the absence of sunlight, alternatively a dark room or a truck for EL signal detection is suitable. But what if you need to use the technology to “extract” the tiny luminescence images mentioned above, from the “heavy” and ”noisy” background that is the sunlight? In 2017, a method to obtain daylight luminescence images of PV modules was discovered [1]. The proposal was based on the polarization of the modules with an AC-modulated bias, correctly synchronized with a camera. Since then, many research groups around the world have continued working in this topic, and recently in the journal Energy Science and Engineering, a paper has being published showing how even in high irradiance conditions, a lock-in technique allows you to perform the imaging process correctly, providing a promising tool in PV plant inspections based on both EL and PL techniques. The technical issues that need to be considered in the imaging process are described there [2].
An EL image may show defects in PV modules like cracks, poor soldering, fabrication issues, and many other common failures that will affect future energy production. It is important that the failure identification and the imaging process are carried out according to IEC 60904-13, guaranteeing the quality of the equipment used, the photographic technique and any further image processing. DNV can help you assess and plan all the necessary steps in the testing process, from initial investigation to the final conclusions about the quality of your PV modules.
[2] Guada M, Moretón Á, Rodríguez-Conde S, Sánchez LA, Martínez M, González MA, Jiménez J, Pérez L, Parra V, Martínez O. Daylight luminescence system for silicon solar panels based on a bias switching method. Energy Sci Eng. 2020;00:1–15.