For photovoltaic (PV) devices to operate successfully over an expected lifespan of 30 years, much research is needed in all aspects of these devices. This study is concerned with the monitoring of the performance and degradation of PV devices over extended periods as well as the effect of meteorological conditions on device performance. The PV devices used in this study comprise different cell technologies and designs. The performance of conventional flat plate modules was monitored over a 15-month period and that of a PV concentrator array over a 13-month period. The results of this performance monitoring are presented in this paper. Degradation mechanisms of PV devices are also discussed. This study showed that, as expected, the power ratings of PV devices do not usually give an accurate indication of their performance outdoors. Results obtained also showed that meteorological conditions could cause an 18% reduction of a module's potential power. A degradation monitoring procedure revealed potential degradation mechanisms, such as mismatched cells, hot spot formation and low cell shunt resistances on some modules. A comparative study on the PV concentrator modules showed that the concentrator modules produced much less energy than their rated energy when operating outdoors. The energy performance of a tracked flat plate module vastly exceeded the concentrator modules' performance.