Implementation of technical specifications to standardise and improve electroluminescence imaging test setups

Abstract

Electroluminescence (EL) is an important tool in photovoltaic (PV) module quality testing and module degradation assessment. EL imaging is primarily a qualitative test that allows for cell cracks and severe damage to be easily identified. Degradation occurs over the lifetime of a module, so it is essential that EL images are recorded in a way that is consistent and comparable to ensure that the degradation is reliably monitored. In order to be able to compare images taken at different labs and over a period of years, the test procedure needs to standardised to ensure that results are comparable. This paper sets out the best practices for lab EL imaging of modules and on-site imaging informed by the Technical Specification (IEC TS 60904- 13:2018) and current research. The quality of the EL imaging results is dependant on the camera used, the test setup factors such as camera position, number of images per module and light conditions. Optimum camera focus is essential for sharp images and a procedure to assist manual focusing is suggested. Five test setups for modules, cells and module-strings are compared, either involving a single camera/image setup or multiple images/cameras. The resolution and sharpness are compared for each setup. The additional cost and/or time involved in the better image resolution needs to be weighed up to the importance of detecting finer defects. If the requirement is to detect major defects then faster, cheaper systems can be used but in order to detect fine cracks and defects the additional cameras or longer testing times are needed.