**2. Materials and Methods**

### *2.1. Electricity Load Data*

This study was conducted in a case study location with an isolated power grid system, i.e., Bali Island, located in Indonesia. Bali's power is provided by external electricity producers from East Java Province and domestic electricity generators within the island. All of the power generated in Bali is utilized solely inside the island's boundaries. As indicated in Figure 1, we are using two-year electricity load data, i.e., 2018–2019. As seen in Figure 1, the electricity demand in Bali follows a consistent pattern throughout the year, with peak demand occurring during January through May and September through November and peak demand occurring during June through August. According to Figure 1, there are anomalies in the power load statistics for both 2018 and 2019, namely, 17 March 2018, and 7 March 2019, which are both Nyepi Days in Bali, during which people in Bali refrain from engaging in any activity, indoor or outdoor, on those days. There was also an electricity interruption on 5 September 2018, which resulted in a total outage of electricity over the whole Bali islands. The daily averaged electrical load and the daily trend is also depicted in Figure 1, which was derived through linear regression. We may also assume from this trend line that the power demand increased from 2018 to 2019. On average, 0.123 megawatts (MW) per day are added to the daily trend line in 2018, and 0.162 MW per day is added to the daily trend line in 2019.

**Figure 1.** Electricity load data in Bali Island during 2018 (**a**) and 2019 (**b**). Hourly, daily, and daily trend electricity load are denoted by red line, blue line with circle, and black dot-dashed line, respectively.

Not only is it vital to examine the yearly trend, but it is also critical to evaluate the daily and weekly variations of the power load in the system under investigation. Figure 2 depicts the weekly and daily variance in electricity demand in Bali for the year 2019. In terms of weekly variation, we can see in the left-hand portion of Figure 2 that the characteristics of electricity demand in Bali remain relatively constant during the weekdays. In contrast, on weekends, there is a slight decrease in electricity demand on Saturday and a slight decrease in electricity demand on Sunday. These features are unsurprising given that most people do not work on Sundays, resulting in decreased electricity demand. The lowest power consumption in Bali is at 4:00 a.m. local time, as seen in the right portion of Figure 2. Still, the highest electrical demand is between 8:00 and 10:00 a.m. local time, when people begin their activities during the day. During the lunch hour, between 12:00 and 01:00 p.m., when most individuals take their lunch break, there was a modest decrease in electricity demand. The most significant demand for power happened between 07:00 and 08:00 p.m. when individuals ate their dinner. These hourly and daily characteristics are crucial to consider when constructing an electrical load forecasting system. In the following subsection, we will discuss the weather data used in this work.

**Figure 2.** Variations of electricity load in Bali during 2019: (**a**) Weekly variation; (**b**) Daily variation. The solid black lines denote the mean value, whereas the gray lines denote the variations.
