Characterization of a Crystalline Silicon Photovoltaic System after 15 Years of Operation in Northern Denmark

The total installed photovoltaic (PV) capacity in Denmark has reached 553 MW at the end of 2013. This exponential boom PV installations, experienced in just the last few years, was mostly focused in the residential rooftop sector (under 6 kWp), and was driven by a generous net-metering scheme and the high electricity price (among the highest in Europe). Although some of the incentives were reduced in 2012, the Danish PV market still remains attractive for commercial PV installations. As a consequence of this rapid growth in PV installations, there is not much experience and data available concerning the long term performance and degradation modes of PV systems installed in Denmark. From a global perspective of the PV system performance and reliability research, there is the initiative to develop comparative testing standards for PV modules, which are climate specific. In this this regard field performance degradation data and understanding of the climate/region specific failure modes of PV modules is necessary. In the present work we investigate the performance degradation of a 15 year old PV system (based on multi-crystalline silicone technology), and aim to identify the main parameters of the PV system that have degraded, as relative to the datasheet values and to a control module which came from the same batch, and was stored indoors during the 15 years. In addition to the degradation analysis of the main parameters of the current-voltage (I-V) characteristic curve (such as short circuit current, open circuit voltage, maximum power voltage and current), performed in many field degradation studies, we also investigate the degradation of the PV generator through the perspective of the diode model parameters, to gain a better understanding of the failure modes affecting the PV system.
In the first part of this study we make a comparative analysis (through outdoor I-V characterization) between the degradation of the two strings constituting the PV system, and reference parameters obtained from datasheet and from the control module, which was in storage. In the second part of the study we analyze the degradation of individual modules within the two strings, through laboratory I-V characterization and electroluminescence imaging, with the goal of identifying the nature and distribution of the failure modes occurring within the PV system