The degradation observed on a 7-kWp Si-x photovoltaic array after 17 years of exposure on the roof of the Solar Energy Institute of the Polytechnic University of Madrid is presented. The mean peak power degradation has been 9% over this time, or an equivalent to 0.53% per year, whereas peak power standard deviation has remained constant. The main visual defects are backsheet delamination at the polyester/polyvinyl fluoride outer interface and cracks in the terminal boxes and at the joint between the frame and the laminate. Insulation resistance complies well with the requirements of the International Electrotechnical Commission 61215 tests
