## 5 Numerical Results
### Results of Wind Power Curtailment Scheduling  
In the solution without wind curtailment, one of the two nuclear units needs to be turned off in order to ensure sufficient downward reserve capacity. While in the case with wind curtailment, as wind generation is reduced, generation levels of the other units can be increased enough so that sufficient downward reserve capacity is ensured. Therefore, both nuclear generators do not have to be turned off.  
Figure 5 shows the number of committed peaking units with and without wind curtailment. In the UC problem with wind curtailment, a fewer number of peaking units need to be turned on for all the time periods. This is because wind curtailment contributes to the mitigation of short-term variations of wind power at night. By incorporating wind curtailment, it is able to compensate for short-term wind variations without any fast responding peaking generator.  
Figure 6 shows the scheduled absolute power limits of the UC schedule with wind curtailment. A portion of wind curtailment is to avoid oversupply of wind generation, which enforces baseload generators to be turned off. Wind curtailment during 4-6 h is attributed to an oversupply of wind generation because an absolute power limit that is set to be the lowest available wind power is sufficient to fully mitigate the wind power uncertainties. The remaining portion of the wind curtailment is attributed to expensive spinning reserves to be scheduled against wind power uncertainty. At 20 h and during 23-24 h, wind generation is curtailed for this reason because there is no need to be concerned about an oversupply during these times.  
Figure 5: Number of committed peaking generators.  
Figure 7 shows the results of the scheduled spinning reserve with and without the implementation of wind curtailment. During 1-8 h, 21 h, and 23-24 h, a lower spinning reserve is scheduled with wind curtailment implemented than that without the implementation of wind curtailment. It can be concluded that the wind curtailment makes it possible to ensure operational security with a lower reserve capacity.  
Figure 8 shows the system ramping capabilities in both cases with and without wind curtailment. By scheduling the wind curtailment, the proposed method provides a UC solution that is capable of compensating for short-term wind variations with lower ramping capability. Because of mitigation of short-term variations, the fast responding peaking units need not replace the baseload units for improving the ramping capability of the system, and this leads to a decrease in the operation cost.  
Figure 6: Scheduled absolute power limit.  
Figure 7: Scheduled spinning reserve with and without wind curtailment: (**a**) upward spinning reserve and (**b**) downward spinning reserve.  
Table 1 summarizes a comparison of the simulation results of generation scheduling in cases that do and do not implement wind power curtailment. The energy cost is generally expected to increase with wind curtailment because significant zero cost wind energy will be wasted. However, the results in Table 1 are in contrast to this expectation. In order to avoid oversupply without wind curtailment, baseload generators may need to be turned off, and other expensive generators need to replace them because of their minimum generation level. Once the baseload generators are turned off, they cannot be brought into operation again soon because of the minimum down time constraint. Consequently, without wind curtailment, more expensive generators need to be scheduled, and this leads to an increase in the operational cost.