The long-term performance and reliability of photovoltaic (PV) modules and systems are critical metrics for the economic viability of PV as a power source. In this study, the power degradation rates of two identical PV systems deployed in Florida are quantified using the Performance Ratio analytical technique and the translation of power output to an alternative reporting condition of 1000 W m−2 irradiance and cell temperature of 50 °C. We introduce a multi-pronged strategy for quantifying the degradation rates of PV modules and arrays using archived data. This multi-pronged approach utilizes nearby weather stations to validate and, if needed, correct suspect environmental data that can be a problem when sensor calibrations may have drifted. Recent field measurements, including I-V curve measurements of the arrays, visual inspection, and infrared imaging, are then used to further investigate the performance of these systems. Finally, the degradation rates and calculated uncertainties are reported for both systems using the methods described previously. Copyright © 2012 John Wiley & Sons, Ltd.