Selection and peer-review under responsibility of the scientific committee of the 11th Int. Conf. on Applied Energy (ICAE2019). Copyright © 2019 ICAE International Conference on Applied Energy 2019 Aug 12-15, 2019, Västerås, Sweden Paper ID: #774 OPTIMAL INVERTER SIZING RATIO FOR PHOTOVOLTAIC POWER PLANTS IN MALAYSIA Keen-Yip Lai 1 , Boon-Han Lim 1* 1 Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Bandar Sungai Long, Kajang, Selangor, Malaysia ABSTRACT 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 1. INTRODUCTION Inverter plays a vital role in a grid-connected photovoltaic (PV) power plant. Its primary function is to convert the generated power in the direct current (DC) form to the alternate current (AC) form. The price of an inverter is usually quoted in dollars per watt. Therefore, the larger the total rated power (called size, but not the physical size) of all inverters, the higher the capital expense of a PV power plant and thus the higher the levelised cost of electricity (LCOE) for the energy generated. During designing a PV power plant, the inverters are usually undersized as compared to the PV plant DC rated capacity, to reduce the capital expense. This technique is allowed if the solar irradiance of a site is mostly less than 1000 W/m 2 [1-2]. Besides, the operation of a PV system is subjected to various performance losses, especially loss due to the temperature effect [3]. Therefore, the performance ratio (PR) is usually less than 0.85 in Malaysia. As such, even if part of the solar irradiance is more than 1000 W/m 2 , undersized is still possible for reducing the LCOE. When the input power of the inverter is beyond the maximum input power of an inverter, the inverter will clip the input power and maintain the output power at its maximum value. The loss of income due to the total clipped energy might be less than the cost saved from the undersized inverter. Since the inverter rated power can be smaller, a specific term called “inverter sizing ratio” (ISR) is used to indicate the ratio of the DC power capacity of the PV array to the AC power capacity of the rated output power of an inverter. The optimal ISR for a PV power plant is affected by many parameters such as characteristic of solar resources, the PR of the system, the efficiency characteristic of an inverter [4, 5] and the performance