-Development of both long lifetime and highly reliable photovoltaic modules and also test methods for characterization of module reliability-
Photovoltaic modules with improved reliability and long lifetime are developed using novel module materials, for example, encapsulant, backsheet, interconnector, sealant, etc. Test methods for characterization of module lifetime are also developed. Both energy yield and reliability for photovoltaic modules set in the outdoor site are characterized.
Photovoltaic modules are fabricated using various apparatuses for commercial size of about 1.5 m. Various novel module materials are examined. Degradation mechanism of photovoltaic modules is studied and various accelerated reliability test methods are also developed based on the degradation mechanism. Various types of commercial photovoltaic modules and newly developed test modules are exposed at the outdoor site and connected with gird. Dye-sensitized and organic photovoltaic modules are also exposed. Those modules exposed are characterized based on material science and device physics.
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. The life prediction of photovoltaic modules and the development of the test methods are also carried out. In addition, as shown in Fig. 2, we developed the plug-in solar for mobile device charging as an emergency power supply for large-scale disasters such as huge earthquakes and torrential rain.
Various types of photovoltaic modules of about 70 kW (about 100 kW in future) are exposed outside as shown in Fig. 3. 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.