Optimum inverter sizing of grid-connected photovoltaic systems based on energetic and economic considerations

Abstract

The optimum sizing ratio of the photovoltaic (PV) array capacity, compared to the nominal inverter input capacity, was determined in grid-connected PV (GCPV) systems from two points of view: energetic and economic. The optimum ratio was determined by both empirical and analytical approaches, and based on two PV arrays connected to their inverters, plus three simulated inverters. The flatness of the optimum-energy region due to the inverter characteristics was decreased when economic factors were taken into account. The energetic and economic optimum sizing intervals were defined as the sizing regions causing less than 1% losses from their corresponding optimum points. Subsequently, a compound optimum sizing interval was proposed to maximise the energy injected to the grid and minimise economic costs simultaneously. The results showed that the GCPV system with lower specific DC power generation (kWDC/kWp) and inverter/module cost ratio presented a wider interval (1.12–1.25) than the interval (1.17–1.19) of the system with higher specific DC power generation and cost ratio, for all the analysed inverters. Finally, the optimum sizing ratio was completed by considering a PV module degradation rate of 1%/year, which resulted in a 10% increase in the optimum sizing ratio for a 20-year lifetime.