## 1 Introduction  
Currently, countries around the globe are developing policies to encourage people to harness power from various types of renewable energy sources to solve environmental problems caused by global warming, such as abnormal temperature rise [1; 2; 3]. Until now, these policies were only focused on the quantity of energy, but future policies will need to be focused on enhancing the stability of the generated power and methods to utilize it [4]. An energy storage system (ESS), which is connected to a grid to store energy during the absence of power generation, is crucial for addressing such problems [5]. Recently, ESSs using lithium-ion batteries (LIBs) have become popular, and are expected to be key in addressing issues such as sudden blackouts caused by unstable power supplies or for control of the power demand [6; 7; 8; 9]. In the case of reclaimed land and reservoirs that are suitable for large power generation (around 100 MW), there have been challenges in connecting the power generation facilities to the main power grid. Such cases have the advantage of increasing the economic feasibility and reducing costs. However, they still create with problems when installed in large-scale renewable energy systems, such as needing to get approval from residents, a lack of reliability of the quality of the generated energy, and the expansion of the blackout area.  
To find an alternative solution for securing a stable energy system, the government and main power distributor changed their target to rural farming areas and energy self-sufficient households/towns. A system with an adequate capacity for photovoltaic system (PVs) and ESSs for household load patterns would become a microgrid renewable energy source that can handle following problems: difficulties in choosing a suitable place for generating renewable energy, environmental issues, difficulty in connecting to the power grid of the main power distributor, and a decrease in power quality due to climate change.  
The government and main power distributor expect that an ideal distributed network will form between connected towns, which is an extended concept of a \"prosumer\" (producer and also consumer) that minimizes production and energy consumption losses to enhance energy self-sufficiency [10; 11; 12; 13]. Then, by analyzing the scale and power usage pattern of each house, an entire island can become a prosumer with energy self-sufficiency [14]. Various environmental conditions of the installation sites should be considered in order to accurately predict the output, which would lead to the optimization of the capacities of PVs/ESS [15; 16].  
An announcement was made by the government, declaring to supply and install 3-kW sized PV systems with an efficiency over 18% to 6700 households around the country in 2019 [17], and by 2017, 220,000 households had already been supplied with a PV system. The price of PVs with 3 kW was set to about $5000, and for a system with less than a 2-kW capacity, the price was set to about $4000. This could show that installing PVs and ESSs on a bigger scale or in a group would be more favorable to minimize the unit cost of the system. If the cost of the main components of PVs and ESSs, such as the module, battery, and power conditioning systems (PCS), can be regulated, then a competitive energy source for households can be realized. A reduction in large-scale nuclear and thermal power generation, as intended by the government, will, in turn, be able to reduce the renewable energy certificate (REC), thus resulting in a minimization of the system marginal price (SMP) rise [18; 19].  
In this paper, a calculation and analysis method of the optimum capacities of PVs and ESSs for rural areas for various load usage patterns is presented. Load patterns and environmental data, such as the insolation of certain areas, were analyzed. Then, we visualized how the optimum capacity of the PVs and ESSs would change in different energy self-sufficiency from 70% to 93%, and obtained the relationship between the capacity of PVs and ESSs.