The proper analysis of PV power plant is one of the most crucial requirement for the development of technology, proper distribution and maintainance. This paper presents analysis and comparision of performance of two grid-connected photovoltaic plants which are situated at the same place but based on different module technologies. the monitored plants are 43 kW grid-connected amorphous-silicon system and 58 kW multicrystelline-silicon grid-connected PV system. The performance indices that are used for comparative study of systems are performance ratio, specific yield, reference yield, capture loss, system loss, system efficiency, PVUSA rating, and performance indicator based on ratio of ac power at PTC to dc power at STC. Three year monitored data from July 2011 to July 2014 since plant commissioned are used for the analysis. Major operation and maintainance issues that have occured during this period are also discussed. © 2014 IEEE.