## 4 Numerical Results
### Case Studies and Discussions  
#### 4.2.1 Optimal Solution Results in the Base Case  
In this section, the CVPP's optimal schedule is determined with Plan 1 of the BC contract in Table 2, the probability of activating reserve energy of 1%, and other input data given in Section 4.1. Figure 8 presents daily PV, WP, and demand curves in the highest probability scenario. The results are presented in Figures 9-13. Note that in the proposed model, the first-stage variables are fixed, while the second-stage variables will change according to the scenarios of uncertain parameters. For simplicity, these figures only represent the second-stage optimal results corresponding to the highest probability scenario with the PV, WP, and load curves depicted in Figure 8.  
Figure 8 shows that during 0:00-4:00, 10:00-16:30, and 22:00-24:00, the available power output of REs in CVPP is relatively high compared to electricity demand. Even from 12:30 to 14:00, PV power alone can provide most customers' electricity needs, and the CVPP's total production during this period can be surplus to nearly 20 MW. So, in the DA contract, the CVPP decides to sell electricity to the grid during these periods (Figure 9). However, the results in Figures 9 and 12 show that CVPP only sells some of the excess power of REs to the market. In detail, from 11:30 to 14:30, not all excess electricity outputs of PV and WP are sold to the market, but a part will be accumulated in the ESS (Figures 11 and 12). Especially from 12:00 to 13:00, the total available power output of PV and WP is about 12 MW more than the demand, but the CVPP's selling power in the DA market is only approximately 1 MW. This is because the DA price during this period is relatively low, only about 60 USD/MWh (Figure 9). The energy accumulated in the ESS will be released to sell to the market between 16:00 and 17:00 at a much higher price, around 85 USD/MWh. Also,  
Figure 10: Base case: The CVPP’s trading strategy in the BE market: (**a**) All scenarios of uncertain parameters; (**b**) The scenario with the highest probability. the ESS will discharge to supply customers from 17:00 to 20:00 when the total available power output of PV and WP is not enough to satisfy customers, and the DA price is very high, even more than 90 USD/MWh (Figure 12). On the other hand, the total production of PV and WP from 4:00 to 9:00 is insufficient to satisfy customers, so the CVPP should buy electricity from the market to compensate for this shortage. However, Figures 9 and 12 show that before this power shortage period, specifically from 2:00, CVPP started buying electricity from the market to accumulate in the ESS. As a result, from 7:00 to 9:00, with electricity prices up to 86 USD/MWh, CVPP's buying power is only approximately 7 MW, much lower than the power shortage of about 15 MW. Also, CVPP can sell electricity to the market at high prices between 9:00 and 10:30, thereby increasing its profits. Then, the CVPP's trading strategy in the BE market is analyzed to evaluate the effectiveness of the proposed model. Note that the proposed model determines the maximum ability of the CVPP to provide reserve energy without affecting the entire trading strategy in the DA market. In this model, all CVPP's trading strategies in the BE market, including contracted upward reserve capacity and non-contracted reserve energy, are assumed to be fully activated. Based on these assumptions, the CVPP's trading strategy in the BE market is obtained and presented in Figure 10.  
Figure 11: Base case: The operating strategy of PV and WP in the highest probability scenario of uncertain parameters. Figure 12: Base case: The ESS operation in the DA market in the highest probability scenario of uncertain parameters. Table 2 shows that in Case 1 of the BC contract, the CVPP needs to ensure that it can always provide upward reserve energy of at least 3 MW from 3:00 to 6:00, from 9:00 to 12:00, and from 14:00 to 17:00. Figure 10a presents the CVPP's upward/downward reserve energy in all scenarios of RESs and demand.