## 3 Analysis of Existing Cases
### Case Study of Target System  
To analyze the electrical energy of the target building, I-Smart of KEPCO, which is the database of the maximum power demand of building, was used to derive the building's maximum power demand, and the month of the year in which that maximum demand occurred, as shown in Table 6. According to our analysis, the highest demand was during July and August. Since nation-wide issues concerning electricity demand are mostly debated and acted upon in August, an economic evaluation of PV and ESS was completed for each time period in August. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Season** & **Off Peak Load Time** & **Mid Load Time** & **Peak Load Time** \\ \hline Spring & 0.05 & 0.07 & 0.1 \\ Summer & 0.05 & 0.1 & 0.17 \\ Autumn & 0.05 & 0.07 & 0.1 \\ Winter & 0.06 & 0.1 & 0.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Seasonal Electricity Rate of the Target Building ($/kWh). \begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Information** \\ \hline Electric power rate & General service (A) (High voltage) \\ Contract demand [kW] & 13,000 \\ Basic Charge [USD] & 7.39 \\ Real demand [kW] & 4124 \\ Monthly base rate [USD] & 30,471.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Information of the Target Building. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Classification** & **Summer, Spring, Autumn** & **Winter** \\ \hline Off peak load time & 23:00–09:00 & 23:00–09:00 \\  & 09:00–10:00 & 09:00–10:00 \\ Mid. load time & 12:00–13:00 & 12:00–17:00 \\  & 17:00–23:00 & 20:00–22:00 \\ Peak load time & 10:00–12:00 & 10:00–12:00 \\  & 13:00–17:00 & 17:00–20:00 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Configuration of Electricity Bill. Analysis showed that, on the 6 th of August, the target building demanded and consumed its maximum power and the maximum value was 4121.16 [kW]. According to KEPCO, which is the main power distributor of the nation, the electricity fee could decrease as the real power demand drop. However, there is a limit on just how much the electricity fee could drop, and this is the concept of \"base rate\". It decreases until the real demand becomes 30% of the contract demand. Real demand was set to 30%, which is 3900 [kW], for economic feasibility, since the contract demand of the target building is 13,000 [kW]. PV with 200 [kW] was selected to cover the difference between 3900 [kW] and maximum power demand of 4121 [kW] measured on August, as shown in Table 6. The PV power was set at 200 kW and generating time was set to be 3 h, which is part of the national strategy. The power generated by PV is calculated by multiplying the capacity of PV, solar charging time, and the average insolation. Table 7 shows the system that is designed with those conditions. The PCS (power conditioning system) was chosen with a capacity of 250 kW, because the market standard is 250 kW; there are no products with 200 kW capacities. In the case of Korea, the average time of PV generation is stated as 3.7 h; hence, this study set the time as 3 h  
The battery degradation rate was set at 1.9%. In general, the time when PV system is capable of generation and, when maximum power demand takes place, are not coincided with each other. With this national strategy, a simulation was done, so that the PV system would charge the ESS during the time period 10:00 h to 14:00 h and then discharge during the period 14:00 h to 18:00 h, which is the time when the maximum demand exceeds the contract demand and it would result in paying for extra charge that main power distributor had set in beforehand, as shown in Figure 1.  
Two strategies, for operating the system implemented with a PV system and ESS, were considered: reducing the base rate by controlling the maximum power demand and reducing the base rate by controlling schedules, so that the ESS would charge during a light load and discharge during maximum load, as shown in Figure 2.