Schematic diagram of cross-sectional structure and degradation factors for crystalline silicon photovoltaic modules are shown in Fig. 1. In order to develop reliable photovoltaic modules with lifetime longer than 30 years required properties for module materials and structures are studied using test modules. Key module materials for improved reliability and long lifetime are studied. Combined or highly-accelerated test methods are also developed. It was confirmed that difference in reliability is found by extending test time or test cycle regulated by IEC. Degradation was accelerated by combination of damp-heat and thermal-cycle tests. It was also found from Fig.2 that the dominant degradation factor by damp-heat test is acetic acid generated by reaction between encapsulant and water vapor. Highly-reliable modules with keeping their initial performances even after extended damp-heat test time by 20 times were also developed.
Various types of photovoltaic modules of about 70 kW (about 100 kW in future) are exposed outside. Outdoor data required for characterization of energy yield, especially for novel-type thin-film photovoltaic modules, are obtained. Current-voltage characteristics of photovoltaic modules set in the outdoor site are recorded every 10 min. Such data are analyzed with obtained irradiance and temperature. Photovoltaic modules using newly developed materials are also exposed at the outdoor site.
Fig. 1 Schematic diagram of cross-sectional structure and degradation factors for crystalline silicon photovoltaic modules.
Fig. 2 Relationship between retention of output power after damp-heat test for 3000 h and acetate ion coccentrain in photovoltaic modules.
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