# V2G Strategies to Flatten the Daily Load Curve in Seoul, South Korea
## 2 Daily Load Curve Evaluation Method
### Grid Impact Analysis Using EV Charge and Discharge Modeling through V2G Strategy  
In Section 2.1, charge/discharge model algorithms for each location at home and work and charge/discharge probability density functions for controlled and uncontrolled modes were proposed. That is, the daily charge/discharge load curve of the electric vehicle battery was calculated considering the charge/discharge probability density function, the initial SOC state of the electric vehicle, the charge/discharge time, and the charge/discharge power per hour.  
The number of electric vehicles was calculated by setting the shares of EVs to 10% and 30% of total vehicles in 2030 and 2040, respectively. Specifically, through the V2G charging and the discharging strategy of the uncontrolled mode and controlled mode, the partial load for charging and discharging of one EV was first calculated, and this value was applied to the total number of electric vehicles for the year in order to calculate the EV charge and discharge load curve.  
In addition, the existing daily load curve in Seoul was calculated based on the results of the load pattern analysis of the acceptance standard of the Korea Energy Management Corporation in 2018 [26]. Figure 9 shows the result of calculating the conventional daily load curve.  
Based on Figure 9, a regression analysis method was applied to calculate the existing load curves for Seoul in 2030 and 2040. In addition, considering the existing load curve and the V2G charge/discharge strategy curve, which reflects the electricity rate system presented in Figures 6-8, the entire partial subsurface curve for Seoul was calculated. A detailed overall flowchart is shown in Figure 10 below.  
Figure 9: Existing daily load curve in Seoul, South Korea.  
According to the flowchart shown in Figure 6, the total load curve was calculated by adding the existing loads in Seoul in 2030 and 2040 and the electric vehicle charge and discharge loads, calculated through the uncontrolled mode, control mode 1, and control mode 2.  
Figures 11-16 show the total load curves for Seoul when adding the V2G daily load curve to the existing daily load curve.  
Figure 11: Daily load curve in Seoul in 2030 (uncontrolled mode).  
Figure 10: Flowchart of daily load curve calculation through V2G strategy in Seoul, Korea.  
Figure 14: Daily load curve in Seoul in 2040 (uncontrolled mode).  
Figure 12: Daily load curve in Seoul in 2030 (controlled mode 1).  
Figure 13: Daily load curve in Seoul in 2030 (controlled mode 2).  
As shown in Figures 11-16, the conventional 2030 and 2040 daily load curves indicate that the load gradually increases from 9:00 a.m., decreases from 12:00 a.m. to 1 p.m., increases from 1 p.m., reaches its peak around 2 p.m., and then gradually decreases from 6 p.m. In the case of the uncontrolled mode, the discharging starts at 6:00 a.m. (discharging time at the workplace), and the load gradually increases from that time. It flattens at 9:00 a.m., and then it decreases. In the case of control mode 1, the load curve shows a similar behavior to the uncontrolled mode, but the discharge load is higher due to the SMP tariff. Control mode 2 is different from control mode 1 in that the discharging load stays high and continues until the grid peak. Overall, the controlled mode associated with the SMP fare has a lower discharge rate in the morning and a higher discharge rate in the afternoon than the uncontrolled mode.