This paper evaluates the performance parameters of five photovoltaic (PV) modules comprising crystalline silicon, multi-crystalline silicon and edge-defined film-fed growth (EFG) silicon technologies. This evaluation was accomplished by measuring and analysing the modules' performances during initial, intermediate and final stages of a 17-month test period. The effect of temperature and irradiance on the performance parameters was investigated. Results obtained indicate that some modules exhibited shunting behaviour and that the EFG silicon module experienced moisture ingress, which in part, resulted in 14% performance degradation. An analysis of the results revealed that the moisture ingress effectively reduced the active module area, resulting in reduced photon absorption, consequently reducing the electron-hole generation as indicated by the reduced short-circuit current. In addition, the EFG-Si module's shunt resistance appeared to decrease over the test period. The rest of the modules showed relatively stable performance, information that is crucial to the system designer and consumer. (C) 2004 Elsevier Ltd. All rights reserved.