The performance of about 400 decentralised PV systems has been evaluated for a period of five years (2001-2006). The systems are situated in the urban area Nieuwland in the town of Amersfoort in the Netherlands and are part of one of the largest decentralised PV projects in the world. The evaluated systems are situated in eight sections and are characterized by different architectural designs, tilt and azimuth angles. In six of the sections the majority of the systems perform well. Data indicate that in those cases there is no substantial lowering of the performance during 5 years. However, several individual systems in those sectors do not perform well. Often defects in the PV system or changes in the roof construction are the cause. For example, string errors are not recognized as such and as a consequence not repaired. In two other sections the performance of the systems is insufficient, but no clear explanation could be found