The problem of energy scarcity has reached a global scale as a result of the majority of energy production relying on non-renewable sources of energy. Solar photovoltaic cells use the photovoltaic effect to convert solar energy into electrical energy. Solar energy can reduce emissions of carbon dioxide (CO2) associated with the generation from fossil fuels as the only CO2 emissions are those embodied in their manufacture. A 268.8 m2 area roof-top grid-connected PV system with a total capacity of 49.92 kWp was installed at Warrenpoint (54.11oN and 6.26oW) in Ireland. One hundred and ninety-two “Renesola” PV modules were installed with a nominal peak output of 260 Wp and efficiency at standard test conditions (STC) of 18.5%. System outputs were measured at 15-min intervals over a year. A system simulation was carried out to predict average annual energy yield, average system efficiency, and average system performance ratio. The system simulation showed that an annual average energy yield of 12,695.2 MJ (3526.4 kWh) was generated at an average system performance ratio of 85% and an average system efficiency of 15.8%. System measurements showed an average annual energy yield of 12,035.8 MJ (3343.5 kWh) at an average system performance ratio of 85.17% and system efficiency of 15.82%. The system performance ratio measured was greater than the performance ratio predicted by system simulation by 0.17%. The system’s measured efficiency was greater than that given by the system simulation by 0.02%. The average annual energy yield (12,695.2 MJ) predicted by the simulation was greater than the system’s measured annual energy yield (12,035.8 MJ) by 659.4 MJ.