Impact of photovoltaic aging on power quality: THD-based evaluation with respect to the IEEE 519-2022 standard

Abstract

Solar photovoltaic (PV) energy is regarded as one of the most promising sources for the transition toward sustainable electricity generation. However, the long-term performance of PV modules is affected by progressive degradation, which reduces not only their power output, but may also alter the power quality of the complete conversion system. This study investigates the long-term effects of the PV module aging on the electrical performance and the current Total Harmonic Distortion (THD_i) of a standalone PV system. Aging is simulated through established degradation laws applied to three key parameters of the single-diode model: the optical transmittance of the semi-transparent upper layer, the series resistance and the shunt resistance. A comprehensive MATLAB/Simulink model, including the PV module, a DC–DC converter, a MPPT controller, a DC–AC inverter, a LC filter, and a resistive load, is used to determine the voltage, the current, the power, and the harmonic spectrum evolution over a 50-year simulation horizon. The combined effects of aging and operating temperature are also investigated. The results show that the PV module output power decreases from 238.5 W in the initial state to 149.1 W after 50 years, corresponding to a loss of approximately 37.5%, while the inverter output current THD_i increases from 2.17 to 13.63%. A configuration-dependent transition occurs between years 32 and 33, when the THD_i rises from 4.51 to 5.91% and exceeds the 5% comparative benchmark adopted with reference to IEEE 519-2022. Elevated temperatures further amplify harmonic distortion in aged operating conditions, with the THD_i reaching 18.87% after 50 years at 75 °C. Frequency domain analysis reveals that the degradation is associated not only with an increase in the overall distortion, but also with a redistribution of spectral energy toward the lower-frequency harmonics, the interharmonics, and the modulation sidebands. This evolution is quantitatively characterized by decreases in the spectral centroid and spectral entropy. These findings demonstrate the potential of combined THD_i and spectral indicators as indirect features for the PV system condition monitoring and the predictive maintenance. Nevertheless, an experimental validation is required before the proposed indicators and the aging threshold can both be generalized to other PV technologies, converter configurations and operating conditions.