Review on Infrared and Electroluminescence Imaging for PV Field Applications
IEA PVPS Task 13, Report IEA-PVPS T13-10:2018, March 2018
Ulrike Jahn, Magnus Herz1, Marc Köntges2, David Parlevliet3, Marco Paggi4, Ioannis Tsanakas5, Joshua S. Stein6, Karl A. Berger7, Samuli Ranta8, Roger H. French9, Mauricio Richter10, Tadanori Tanahashi11
1 TÜV Rheinland, Cologne, Germany; 2 Institute for Solar Energy Research Hamelin, Emmerthal (ISFH), Germany ; 3 Murdoch University, Perth, Australia; 4 IMT School for Advanced Studies Lucca, Italy, 5 Interuniversity Microelectronics Centre (IMEC), Leuven, Belgium; 6 SANDIA National Laboratory (SNL), Albuquerque, NM., USA; 7 Austrian Institute of Technology GmbH, Center for Energy (AIT), Austria; 8 Turku University of Applied Sciences, Finland, 9 Case Western Reserve University, Cleveland, OH,USA; 10 3E, Belgium, 11 National Institute of Advanced Industrial Science and Technology (AIST), Japan
The quality assurance measures for PV modules are of fundamental importance for any PV power plant asset. The failure-free operation of the PV modules is a prerequisite for efficient energy production, long life, and a high return on the investment. During operation PV modules may develop defects which can be repaired if they are detected in time, but they can cause a severe drop in energy production and sometimes safety issues. To ensure the operation of the PV modules without significant losses, fast and reliable methods to evaluate the performance of the photovoltaic modules are required, both during the production process and after the installation of the PV modules. For that reason more and more EPC and O&M companies offer regular infrared (IR) and electroluminescence (EL) imaging inspections of PV plants to ensure the safety and high performance of the PV array in addition to IV curve measurements and monitoring. IR and EL are two imaging techniques, which identify faults and problems developing with PV modules.
The use of infrared (IR) imaging for the evaluation of PV modules has many advantages. First of all, a great number of failures developed on PV modules can be detected using IR imaging, from hot-spots to mismatch losses or installation failures. Furthermore, IR imaging technique can be applied for non-destructive testing and used to scan installed PV modules during normal operation. Finally, thermal cameras also allow scanning large areas within a short time frame.
The optimized operation of the PV cell is to absorb the light and convert it into electricity. However, due to reciprocity principle the opposite is also possible and offers the opportunity of Electroluminescence (EL) imaging. Electroluminescence is a phenomenon that has been used for a long time for other applications such as lightening, but recently has been introduced as an investigation procedure for PV modules and strings. It consists of applying a direct current to the PV module and measuring the photoemission by means of an infrared-sensitive camera. EL imaging provides insight into micro cracks and other defects within the cell material. This in turn helps identify faults and problems present or developing within the PV module.
In this report, we present the current practices for infrared (IR) and electroluminescence (EL) imaging of PV modules and systems, looking at environmental and device requirements on one hand, and on the interpretation of sample patterns with abnormalities on the other hand. The goal is to provide recommendations and guidelines for using IR and EL imaging techniques to identify and assess specific failure modes of PV modules and systems in field applications.
This report provides a comparison of the relative merits of EL and IR imaging techniques. These types of optical measurement provide fast, real-time and high resolution images with a two-dimensional distribution of the characteristic features of PV modules. IR imaging measurements of the thermal behaviour of cells in a module allows a number of defects to be easily and quickly identified. These include short circuits in solar cells, shunts, inactive cell parts and PID. However, not all the failures of PV modules lead to an increase in temperature. Taking this into consideration, the IR measurements alone cannot identify all the types of failures. On the other hand, PV modules with clear EL-images sometimes provide IR-images with hot areas. A combination of both techniques quickly detects the most common defects in a PV module with high accuracy and provides a good indication of the health and reliability of the PV modules within a plant.
The Technical Report can be downloaded from the IEA-PVPS website www.iea-pvps.org