A comparative analysis of central and string inverters for utility scale photovoltaic plants : cost, efficiency and performance

Abstract

Central inverters have traditionally dominated utility-scale solar farms due to their high efficiency, reliability and simplified maintenance, but they face limitations in scalability and flexibility. String inverters, initially used in residential applications, have evolved for utility-scale PV plants thanks to higher-capacity units, improved power electronics, and enhanced modularity, achieving DC-to-AC conversion efficiencies of up to 98%. This thesis presents a comparative analysis of central and string inverters for utility-scale PV plants, focusing on performance, energy yield, and cost-effectiveness. Full plant designs and PVSyst simulations were conducted for two contrasting climates: Helsinki, Finland, and Garoua, Cameroon, evaluating fixed-tilt and single-axis N-S tracking systems under shaded and unshaded conditions. Results showed that, string inverters slightly outperformed central inverters in high-irradiance regions, with annual energy gains of up to 1.08% in Garoua, while in low-irradiance Helsinki, gains are modest (0.64 –1.03%). Switching to N-S tracking further increased the energy yield for both inverter types. The findings demonstrate the growing viability of string inverters for utility-scale PV plants. Insights aim to support decision-making in the design and operation of next-generation PV plants.