Long-term examinations up to 20 years of performance ratio and degradation rate of different-type photovoltaic modules at central part of Japan

Performance ratio and degradation rate of various-type silicon-based photovoltaic modules, which are multi-crystalline silicon, amorphous silicon, amorphous silicon/multi-crystalline silicon tandem, and amorphous silicon/amorphous silicon germanium/amorphous silicon germanium three-stack, were investigated after long exposure period up to about 20 years from 2000 to 2020 at outdoor site in Shiga-prefecture, Japan. Moreover, meteorological elements such as ambient temperature, and solar irradiance at outdoor location were investigated for approximately 20 years. Outdoor spectral distribution was observed in a year. It is disclosed that monthly performance ratio of multi-crystalline silicon module is inversely proportional to ambient temperature, whereas that of the amorphous silicon and tandem modules is positively proportional to ambient temperature. Degradation rate of the amorphous silicon module is the highest (3.776 %/year), and that of the tandem module is the second highest (1.338 %/year) of all silicon-based silicon modules after light exposure in the first period of the installation of the modules (≤10 years), implying performance ratio of amorphous silicon and tandem modules are more decreased than other type (multi-crystalline silicon and three-stack) modules. With longer years of the installation up to 20 years, degradation rate of each type of the modules is further decreased, suggesting that silicon-based modules become more stable after longer light exposure time.