Long Term Performance of PV Modules: System Optimization through the Application of Innovative Non-Destructive Characterization Methods

Abstract

AIT Austrian Institute of Technology, Energy Department, Vienna OFI Austrian Research Institute for Chemistry and Technology; Franz Grill Strase 5, Objekt 213, 1030 Wien, Austria. T: +43-1-7981601-250 F: +43-1-7981601-303 yuliya.voronko@ofi.at; gabriele.eder@ofi.at http://www.ofi.at ABSTRACT: Innovative and highly sensitive analytical tools for the non-destructive detection and visualization of defects, delamination and material incompatibilities within the multi-material laminate of a PV-module are presented. The presence and position of physical imperfections such as delamination, voids or impurities within a module were determined with Pulse Thermography (PT) and Scanning Acoustic Microscopy (SAM). With SAM it is also possible to identify cracks within a wafer very accurately, as could be demonstrated in a comparative measurement with Electroluminescence (EL) experiments. For the non-destructive identification of chemical changes in the individual layers of a PV-module - caused by degradation, decomposition or impurities - confocal Raman microscopy has proven to be a very powerful tool. Keywords: PV module reliability, characterization, interfaces, scanning acoustic microscopy, pulsed thermography, Raman spectroscopy 1 INTRODUCTION Reliability and long term performance of PV modules over up to 25 years are key demands of the market to allow photovoltaic to play an increased role in the future energy supply system. Therefore, modules should be subject not only to electrical performance tests conforming to standards but also to quality assurance testing in regard to the chemical, optical and physical properties of the materials and laminates used. In reality, however, this characterization is a very demanding task as there are only limited tools available which allow non-destructive analysis of materials already embedded in PV-modules. But this is exactly what is needed for pre delivery inspection at the manufacturing company or in the case of performance problems at the power plants (failure analysis). Thus, our research activities were focussed on the development of innovative and sensitive analytical methods that allow for the investigation of materials, PV-components and modules without destroying them. In order to evaluate these analytical techniques on well-defined model systems, a set of mini-modules was manufactured and applied to various accelerated aging tests (including the influence of air pollutants). By analysing the mini-modules before and after the accelerated aging procedures, we obtained a clear detection and visualisation of the aging induced changes in the chemical and physical properties of the PV modules. As a next step, the correlation of the occurrence of these aging induced defects with the module performance will be investigated. 2 EXPERIMENTAL For the visualisation and detection of imperfections, voids and defects within the multilayer structure of complex laminates,