## 4 Case Study
### Economic Analysis of the MSTS Retrofit Scheme for Thermal Power Units Under RLVs  
To compare the proposed TPUMSTSR model under RLVs with the conventional single flexibility retrofitting model, CS 4 from the MCS setup is selected for case study simulation analysis. The case study includes the following three flexibility retrofitting schemes:  
**Scheme 1**: Thermal power undergoes independent RLV retrofitting, with a maximum achievable ramp rate of 1.8 \(P_{\text{N}}\)/h for conventional PR and 0.9 \(P_{\text{N}}\)/h for DPR. **Scheme 2**: Thermal power undergoes independent MSTS retrofitting, with rated capacities of 200 MWh for both high-temperature and low-temperature storage, a heat storage and release efficiency of 98.5%, a thermal-to-electric conversion efficiency of 40%, \begin{table}
\begin{tabular}{c c c c} \hline
**Power Source** & **Thermal Power Capacity (MW)** & **PV Power Station Capacity (MW)** & **Wind Power Plant Capacity (MW)** \\ \hline CS1 & 200 + 300 & 200 & 300 \\ CS2 & 300 + 300 & 120 & 180 \\ CS3 & 300 + 600 & 200 & 200 \\ CS4 & 600 + 600 & 400 & 300 \\ \hline \multicolumn{4}{c}{IPP 1-5 Thermal Power Capacity (MW)} \\ \hline IPP 1 & IPP 2 & IPP 3 & IPP 4 & IPP 5 \\
1040 & 508 & 687 & 580 & 564 \\ \hline \end{tabular}
\end{table} 
Table 1: Generation settings of the test system. \begin{table}
\begin{tabular}{c c c} \hline
**Parameters** & **Explanations** & **Value** \\ \hline \(A_{1}\), \(A_{2}\) & Different allocation tiers & 0.7/0.8 \\ \(\mu_{1}\), \(\mu_{2}\) & The load rates corresponding to compensation thresholds & 0.5/0.4 \\ \(z_{1}^{\text{TPU}}\), \(z_{2}^{\text{TPU}}\), \(z_{3}^{\text{TPU}}\) & Correction coefficients for thermal power & 1/1.5/2 \\ \(k_{\text{m}}^{\text{TPU}}\) & The PR revenue correction coefficient & 0.5/1 \\ \(z_{t}^{\text{WT,S}}\) & The wind power output correction coefficient & 0.8/1.6 \\ \(z_{t}^{\text{PV,S}}\) & The PV output correction coefficient & 1/2 \\ \(C^{\text{GU}}\) & The penalty factor & \(5\times 10^{4}\) (CNY/MW) \\ \(C^{\text{WT}}\), \(C^{\text{PV}}\) & The unit revenue of wind and PV power generation & 850/740 (CNY/MW) \\ \(C^{\text{OB}}_{t,e}\) & The maintenance price per cycle for the TPUMSTSR system & 10 (CNY/MWh) \\ \(\mu^{\text{WT}}\), \(\mu^{\text{PV}}\) & The minimum utilization rate of the unit & 0.85/0.80 \\ \(C_{0}\), \(C_{1}\), \(C_{2}\) & The unit electricity sales prices corresponding to different compensation thresholds & 375/400/1000 (CNY/MW) \\ \(C^{\text{coal}}_{t}\) & The unit price of coal per ton & 685 (CNY/t) \\ \(C^{\text{TE}}_{t}\) & The unit treatment cost & 1.2 (CNY/kg) \\ \(C^{\text{RED}}\) & The curtailment cost for wind and PV power & \(10^{4}\) (CNY/MW) \\ \(\tau_{i,u}^{\text{TPU}}\) & The coefficient of adjustable flexible resources of the unit & 0.4 \\ \(C^{\text{IB}}_{t,e}\) & The initial investment cost & 4,912,600 (CNY/MWh) \\ \(V^{\text{CL}}_{i,e}\) & The total number of life cycles & 20,000 times \\ \hline \end{tabular}
\end{table} 
Table 2: Parameters used in the CS. and maximum heat release coefficients of 0.29 and 0.39 for high-temperature and low-temperature storage, respectively. **Scheme 3**: TPUMSTSR under RLVs, with RLVs and thermal storage parameters based on those in Scheme 1 and Scheme 2. To maximize CS profit, the Gurobi solver is employed to solve the day-ahead optimal scheduling model for a single CS. The various output curves for the 48 time periods from 00:00 to 24:00 are shown in Figures 6-8, while the optimization results for the three retrofitting schemes are summarized in Table 3.  
The following conclusions can be drawn based on the aforementioned figures and tables:  
When thermal power units undergo only RLV retrofitting, their maximum ramping rate between adjacent time periods reaches 9.29 MW/min, significantly improving their real-time ability to accommodate renewable energy. However, the coal consumption and operational maintenance costs under RLVs are relatively high.