Undersize the capacity of a solar inverter is a common practice in the industry to reduce capital expense. However, the optimal inverter sizing ratio (ISR) is a site- and system-dependent value. It can vary from 1.0 to 2.2, globally. So far, there is no study on the optimal ISR for photovoltaic (PV) power plants in Malaysia. The industrial practice assumes that the ISR is either the inverse of the performance ratio of the system or value of experience design from other countries, which do not share the same climate. In this paper, a generalised method, which separates the system-dependent and non-system-dependent values, is used to find the optimal ISR for eight different geographic locations in Malaysia. The chosen sites are distantly distributed and have different annual solar irradiation. Hourly solar irradiance data is used to find out the power clipped by the undersized inverter during high solar irradiance period. In addition, the simulation also considers the inverter can be overloaded to 110% of its rated capacity, which is a common specification of an inverter nowadays. This feature was not considered in other research articles. The optimal ISR for the eight sites, which was obtained based on the lowest the levelised cost of electricity (LCOE), falls within 1.475 to 1.525. The optimal ISRs show a strong linear correlation with the annual solar irradiation of the sites. The information is useful for the local industry to optimise the LCOE for their project quickly.
Keywords inverter sizing ratio, photovoltaic, solar irradiance, tropical region, grid-connected, inverter size