Title:	Dark IV-Curves as a Method for in Situ Module Characterisation
Author(s):	J. Fröbel, B. Jäckel, M. Pander, U. Zeller
Keywords:	Defects, PV Module, Dark-IV
Topic:	Photovoltaic Modules and BoS Components
Subtopic:	PV Module Design, Manufacture, Performance and Reliability
Event:	38th European Photovoltaic Solar Energy Conference and Exhibition
Session:	4BO.4.3
Pages:	589 - 593
ISBN:	3-936338-78-7
Paper DOI:	10.4229/EUPVSEC20212021-4BO.4.3
Price:	0,00 EUR
Document(s):	paper, presentation

Abstract/Summary:

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For PV module characterization and intermediate assessment during a long-term stress test, the test has typically to be interrupted and the modules are brought to standard test conditions, which brings a number of disadvantages. The interruption of the test inevitably involves temperature changes and relaxation time. It is not possible to measure several test specimens at the same time, and the measurement is performed without the presence of the load. Therefore, methods are being considered to obtain information in-situ about the condition / health of the sample during the stress test. Measuring the dark IV curve of PV modules is a method to obtain information about the current state of the module even during an ongoing stress test. Depending on test conditions and setup dark IV curves can be measured easily. However, care must be taken not to influence sample temperature or to induce other degradation due to external applied voltages. Dark IV in-situ measurements generally allow detection of parameter changes (current I and voltage V) and thus in-situ analysis of tests with changing stresses, such as thermal cycling, humidity freeze, damp heat, PID degradation/recovery, LeTID or cyclic mechanical loading tests with a high number of cycles can be performed. The information gain depends on type of defect and not all defects can be detected as for example cell cracking and current mismatching of strings. Nevertheless, various types of defects found in the light IV curves of a module can be detected by dark IV curve. The change in shunt resistance during PID testing or the changes of the module during LeTID testing can be well tracked utilizing dark IV in-situ measurements. Defective bypass can be analyzed during the stress test while checking reverse voltage dependence of dark IV curve. This procedure is also easily applicable outdoor to assess larger quantities of modules regarding defective bypass diodes. Some defects that are easily visible in light IV curves and Electroluminescence (EL) are not easily detectable by the dark IV curves. Therefor conversion methods for temperature and irradiance should be used with care but can add information overall. Generally, dark IV curves offer the possibility to obtain data with higher temporal resolution, independent of timeconsuming intermediate measurements and allow therefor to monitor stress tests in more detail and possibly detect defects and degradation earlier. From this, improved stress models can be developed, e.g., to more accurately answer questions about the number of maximum stress cycles, i.e., when solder joints break, or whether degradation converges, i.e. during PID- recovery or extended LeTID tests.