PV module defect detection by combination of mechanical and electrical analysis methods

The lifetime and reliability of photovoltaic modules (PV modules) is influenced by defects which have their origin either in manufacturing processes or in operation exposure. Characterization of PV modules is necessary for manufacturers to assure their warranty and to observe process difficulties during production process and for improving their modules during development processes. For customers PV module characterization is important to observe output performance of their PV system and to proof intactness of single modules. For this purpose reliable and nondestructive testing methods are desirable. This contribution gives an overview over PV module defects detected by different characterization methods. By comparing the different methods their suitability to detect certain defects is assessed. Some methods are already standard in solar cell inspection like electroluminescence or thermography and are used on module scale in this work. Other methods like Laser-Doppler vibrometry are used for mechanical purposes and shall be used to determine mechanical parameters of PV modules as a mechanical element. The expansion of these methods by further analysis techniques like digital image correlation techniques allows a very precise assessment of the mechanical and electrical capability which is essential for reliability and lifetime concepts. The observed defects are classified according their origin and their consequences on the overall performance of the device were checked. The influence of alternating thermal loads is presented exemplarily on an unframed thin-film test module.