For the estimation of energy output from photovoltaic (PV) modules, considering the impact of degradation is essential. In this study, the longtime outdoor performance of various types of silicon-based PV modules [single crystalline Si (sc-Si), multi crystalline Si (mc-Si), amorphous Si (a-Si), a-Si/micro crystalline Si tandem, and a-Si/a-SiGe/a-SiGe three-stack (3-stack)] which were installed at the same outdoor exposure condition in Shiga Prefecture, Japan were investigated using Performance Ratio (PR) as an index of performance of PV modules for ten years from 2000 to 2009. Yearly PR and monthly PR were analyzed and degradation rates (DR) were calculated. The DR was different on the kinds of PV modules from 0.404 to 3.51%/year. The a-Si PV module showed the largest DR and the 3-stack PV module had the least trend to degrade. The analysis of the monthly DR indicated that the high DR of the a-Si PV module was due to the quite large DR in summer, whereas the monthly DR of sc-Si and mc-Si PV modules did not differ much from each other throughout the years. (C) 2013 Elsevier Ltd. All rights reserved.