# Utilizing Energy Storage for Operational Adequacy of Wind-Integrated Bulk Power Systems
## 4 Application of the Proposed Operational Adequacy Framework
### Impact of ESS Operating Strategies on Operational Adequacy  
An ESS can be owned by the utility, the wind farm owner, or by an independent entity. The utility-owned ESS will likely be used to reduce the operating costs after maintaining the reliability of the system and meeting environmental compliance. The wind farm operator will coordinate the operation of its ESS with the wind generation to meet its commitments and maximize energy sales. On the other hand, an independently owned ESS will operate to maximize revenues from available components of an electricity market. The operating strategies will, therefore, vary depending on the  
Figure 8: Impacts of wind and energy storage on operational adequacy. ownerships and objectives, and as a result, will have different impacts on the operating adequacy of the power system. A study was therefore carried out to demonstrate the impact of different ESS operating strategies on the operational adequacy of a power system integrated with wind power and energy storage. The test system shown in Figure 4 and described in Configuration 3 of the previous study is used in this study. Two ESS operating strategies, termed as wind-coordinated strategy and grid-supported strategy, are considered for comparative studies. It should be noted that these two are representative cases of several possible ESS operational strategies. Wind-coordinated (WC): This operational strategy considers coordination between a wind farm and an ESS. These can be owned by the same owner or different owners in a coordination agreement. ESS is coordinated with a wind farm to be charged when available wind generation exceeds the commitment. Grid-supported (GS): This operational strategy considers coordination between wind farm, ESS, and utility or system operator which controls grid power access. ESS coordination with wind and grid power support for ESS is simple if the system operator owns both the wind farm and ESS. If they are separately owned, it requires an additional agreement between themselves and the system operator. ESS uses the grid power, usually, during off-peak hours and coordinates with wind farms during the rest of the hours for charging. The evaluation period is divided into three different periods, as shown in Table 3, based upon the net load (forecasted load--expected wind generation) of an hour, to simulate the operating strategies of ESS. Figure 9 demonstrates the coordination strategy for the operation of a wind generation farm and an ESS system. Figure 10a shows that the grid-supported ESS operational strategy results in better operational adequacy of the system compared to the wind-coordinated ESS operational strategy. With this operational strategy, the resultant operational adequacy of LOLP = 0.00112 is better than the benchmark value by almost 15% when Regime 1 is considered. This is possible as ESS can accumulate enough charge irrespective of the initial state of charge of the energy storage with this strategy. Besides, the number of hours when ESS needs to discharge are effectively reduced in this strategy. This allows ESS to perform better in supporting the wind generation and mitigate the loss of load events. However, it needs to be acknowledged that the grid-supported strategy uses a higher number of conventional generators, thereby resulting in higher emissions and operational costs compared to the wind-coordinated strategy, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Periods** Strategy & **Wind-Coordinated** & **Grid-Supported** \\ \hline Peak hours & 6 h with the highest net-load & 6 h with the highest net-load \\ Off-peak hours & Remaining hours & 8 h with the lowest net-load \\ Moderate hours & Remaining hours & Remaining hours \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Different periods of operational strategies. Figure 9: Wind generation and ESS coordination in grid-supported (GS) and wind-coordinated (WC) ESS operational strategies. as illustrated in Figure 10b.