Owing to the diverse photovoltaic (PV) systems available commercially, ranging from the stationary silicon-based PV panels to 2-axes tracker concentrated photovoltaic (CPV) systems and dynamic nature of meteorological data, energy planners and PV system designer require a simple but accurate methodology to understand the economic viability of a renewable solar PV plant. An electrical rating methodology is proposed for evaluating the long-term performance for assorted PV systems, providing a common “playing field” to consumers, planners and manufacturers of PV systems. Given a meteorological condition, the output-based approach or electrical rating of renewable energy system is the key for economic and environmental CO2 emission evaluations. Despite the overwhelming catalog data furnished by PV manufacturers, the long-term electricity rating of a PV system is deemed to be a quick and accurate method for the evaluation of economic viability and the determination of plant sizes and power production from a PV facility. This paper presents and analyses the long term performances, as monthly and overall electrical ratings in kWh/m2.year of two concentrated photovoltaic (CPV) prototypes, the mini dish Cassegrain-type and the Fresnel lens CPVs with triple-junction solar cells, operating under the meteorological conditions of Singapore and compares performances with the other photovoltaic systems.