## 6 Case Simulation
### Economic Benefit Analysis of Power Generation  
A reasonable peak-valley feed-in tariff structure can fully stimulate the enthusiasm for peak regulation of water storage, thus alleviating the tension between the supply and demand of peak-load electricity. Due to the large tariff gap at different times, it is necessary to schedule the complementary system so that each power source can generate more power when the tariff is higher. The grid time-sharing tariff policy adopted in this paper is shown in Table 8.  
With the objective of maximizing generation benefits in the complementary system, Table 9 compares the power generation revenues between pumped-storage retrofitted and non-retrofitted systems under four operational scenarios. Compared with the system without pumped-storage retrofitting, the complementary system with pumped storage achieves an increase in power generation benefits by 5.13% to 6.22%. This improvement is attributed to the operation of pumped storage units following a \"valley pumping-peak generation\" strategy, which enables electricity price arbitrage. During low-price periods, excess wind and PV output is converted into stored water energy, which is then used to generate electricity during high-price periods to fill the power gap. This effectively redistributes the output of wind and PV resources, thereby enhancing the overall power generation benefits of the system. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Scenarios**} & \multicolumn{2}{c}{**Deviation Power (MWh)**} & \multicolumn{2}{c}{**Surplus Water (10\({}^{4}\) m\({}^{3}\))**} \\ \cline{2-5}  & **With Pumped** & **Without Pumped** & **With Pumped** & **Without Pumped** \\  & **Storage** & **Storage** & **Storage** & **Storage** \\ \hline Cloudy and windy & 0 & 67.51 & 0 & 626.4 \\ Sunny and windy & 0 & 67.51 & 0 & 767.8 \\ Cloudy and less windy & 0 & 44.88 & 0 & 709 \\ Sunny and less windy & 0 & 40.58 & 0 & 928.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of operation results for systems with/without pumped storage. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Peak Load** & **Flat Load** & **Valley Load** \\ \hline \multirow{3}{*}{Periods} & 10:00–15:00 & 7:00–10:00 & \\  & 18:00–21:00 & 15:00–18:00 & 23:00–7:00 \\ \cline{1-1}  & 18:00–21:00 & 21:00–23:00 & \\ \cline{1-1} \cline{2-4} \cline{2-4} \cline{2-4} \cline{2-4  
The annual power generation of the complementary system is 5309.71 MWh, with a total income of CNY 218.936 million, and the overall operation economy is good. Carbon emission reduction is 281,500 tons, which has certain environmental significance. The overall system benefits are calculated and presented in Table 12.  
After the pumped storage retrofit, the total life-cycle cost of the system increased by CNY 2.1368 million. However, the total power generation revenue increased by CNY 116.709 million, making it possible to recover the investment and demonstrating strong overall economic performance. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Costs** & **Quantity** & **Capacity** & **Unit Cost** & **Total Cost** \\  & **(MW)** & **(CNY 10,000)** & **(CNY 10,000)** \\ \hline
\begin{tabular}{c} Pumped storage retrofitting cost \\ Operation and maintenance cost \\ \end{tabular} & \(\begin{array}{c}1\\ \backslash\end{array}\) & \(\begin{array}{c}16\\ \backslash\end{array}\) & 160 & 160 \\  & \(\begin{array}{c}\backslash\end{array}\) & 8 & 80 \\ \hline \hline \end{tabular}  
Assuming an even annual distribution of the four scenario types, the power generation benefits of the system are shown in Table 11.  
\end{table} 
Table 10: Initial construction cost. \begin{table}
\begin{tabular}{c c} \hline \hline
**Type** & **Price** \\
**(CNY 10,000)** \\ \hline
\begin{tabular}{c} Initial construction cost \\ Total life-cycle cost \\ Power generation benefit \\ Total increase in revenue \\ \end{tabular} & 240 \\  & 213.68 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Overall economic benefits.