RESEARCH ARTICLE Annual degradation rates of recent crystalline silicon photovoltaic modules Tetsuyuki Ishii1* and Atsushi Masuda2 1 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa 240-0196, Japan 2 National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba-shi, Ibaraki 305-8568, Japan