Online monitoring of power extraction efficiency for minimizing payback period of solar PV system

DC-link electrolytic capacitors are used in single phase solar PV inverters to suppress second harmonic and switching voltage ripples. Electrolytic capacitors are less reliable than other components of PV system. Degradation of these capacitors affects the performance of the system. Reduction in capacitance and increase in equivalent series resistance (ESR) due to ageing increases ripples in dc voltage. Among the ripples present, second harmonic voltage ripple dominates. DC-link voltage ripple causes oscillations in PV operating point thereby reducing PV power extraction efficiency. Technique for online monitoring of PV power extraction efficiency is proposed in this paper. Electrolytic capacitor is selected for power extraction efficiency greater than 99%. Replacement of capacitor is suggested based on deterioration in extraction efficiency. However, frequent replacement of capacitor increases cost of maintenance. Therefore, optimal value of extraction efficiency is determined in this paper, at which total payback period including maintenance cost is minimized. Detailed simulation studies are carried out using Simulink and results are included. Analysis on the payback period for the proposed scheme is presented in this paper.