Degradation of photovoltaic systems based on long-term measurements and laboratory tests
Abstract
Results of the analysis of long series of measurements of photovoltaic (PV) plants in Switzerland are presented. The tree PV systems, Jungfraujoch, 3'450 m a.s.l (Alps), Mont-Soleil, 1'270 m a.s.l. (Jura) and Tiergarten, 530 asl. (Swiss Basin) are part of the long-term measurement program of the Photovoltaic Laboratory (PV LAB) at the Bern University of Applied Sciences BFH in Burgdorf (Switzerland). The focus of the long-term measurement program is the question of the effective degradation of photovoltaic plants that have been in operation for more than 20 years, representing different climatic zones in Switzerland. The findings provide essential information about aging-related power losses of PV systems. The PV LAB of the BFH in Burgdorf (Switzerland) has been measuring numerous PV systems since the 1990s. Based on these long-term measurements, the power losses of the Mont-Soleil, Jungfraujoch PV plants and the plant on the roof of the BFH in Burgdorf were analyzed. For the period 2001-2014, the calculated annual degradation was 0.39 % for the Mont-Soleil PV plant (1'270 m a s l. in the Jura). Further investigations must be made on this system i to exclude influences such as snow and inverter shutdowns, which disturb the calculation of the degradation. The degradation of the plant on the roof of the BFH in Burgdorf was 0.08%. With the relatively long data series from 1995 to 2014 of the PV plant Jungfraujoch (3'450 m a.s.l. in the Alps) an annual degradation of 0.11 % could be found. This value was confirmed with a plausibility test based on flasher measurements and electroluminescence in the laboratory. - The modules used by the BFH from the 1990s aged much less than the modules from a study of the HTW Berlin in 1999 (Quaschning et al., 1999), and that the mechanical structure of PV modules is therefore not insignificant. - It seems that the solar radiation has a very small influence on the aging of the PV cells, because with only 0.11% power loss per year on the Jungfraujoch, where the solar radiation is 1.45 times higher than on the Mont-Soleil, the power loss would have to be greater be. - That other influences than the intensity of solar radiation are important for the aging of the PV modules, such as the - Operating temperature - Moisture (if the PV cells get moist -> "Packaging" of the cells) - Material properties of the modules (glass, plastics, adhesives, etc.). Looking at the degradation of the three plants (25 years of operation), it is noticeable that they are below the 0.8% reported in the literature for all three plants (ca. factor 8 smaller). This means that these plants produce more than specified after the 25 years. For the Mont-Soleil plant, the year 2012 was omitted due to inverter failure from the evaluation. Nevertheless, the highest degradation can be found here. This comes from snow damage. The modules were mounted without frame and therefore are no longer in the warranty conditions.