## 4 Case Study
### Simulation Results and Analysis  
The results of low-carbon economy dispatch under six scenarios are shown in Table 3.  
As can be seen from Table 3, the electric output of the CHP unit is restricted because of \"determining electricity by heat\" and cannot be lowered, which results in a large amount of wind abandonment in Scenario 1. In Scenario 2, the total system cost is reduced by 3.03% after the introduction of P2G, mainly due to the absorption of a large amount of excess wind power during the wind abandonment period, which reduces 56.85% of the wind abandonment penalty cost. However, due to the need to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scenario** & **With CCS** & **With P2G** & **With Heat Recovery** \\ \hline
1 & \(\times\) & \(\times\) & \(\times\) \\
2 & \(\times\) & \(\surd\) & \(\times\) \\
3 & \(\times\) & \(\surd\) & \(\surd\) \\
4 & \(\surd\) & \(\times\) & \(\times\) \\
5 & \(\surd\) & \(\surd\) & \(\times\) \\
6 & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Module settings of each scenario. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Scenario** & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline Total cost/\(10^{4}\$\) & 215.66 & 209.12 & 204.32 & 216.85 & 197.29 & 192.87 \\ Coal-fired units operating cost/\(10^{4}\$\) & 90.77 & 90.76 & 90.76 & 93.35 & 93.23 & 93.20 \\ Gas purchase cost/\(10^{4}\$\) & 69.03 & 67.82 & 65.91 & 64.41 & 63.10 & 60.74 \\ Carbon purchase cost/\(10^{4}\$\) & / & 4.04 & 3.86 & / & 0 & 0 \\ Wind abandonment cost/\(10^{4}\$\) & 16.50 & 7.12 & 5.63 & 16.50 & 5.41 & 3.77 \\ Transmission and storage cost/\(10^{4}\$\) & / & / & / & 10.13 & 7.62 & 8.12 \\ Carbon trading cost/\(10^{4}\$\) & 39.38 & 39.38 & 38.17 & 32.47 & 27.93 & 27.04 \\ Methane production/m\({}^{3}\) & / & 71,462 & 68,317 & / & 83,819 & 80,103 \\ Carbon emissions/t & 8503.37 & 8501.16 & 8339.21 & 7615.59 & 6917.02 & 6731.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Low-carbon economics dispatch results of different scenarios. Figure 6: Output power of gas load. constraints, the electric output of CHP units cannot be further reduced at this time, and wind abandonment still exists. In Scenario 3, heat recovery of P2G is considered. P2G can not only generate income by using unused wind power to produce methane, but also inject residual heat from methanation into the heat network. P2G and its heat recovery relieved the heating pressure of CHP units and further reduced the forced electrical output, thus reducing the wind abandonment of the system. However, this also reduced the wind abandonment available for P2G to some extent and reduced the methane production of P2G by 4.4%. In Scenario 3, when wind curtailment exists, the system will preferentially use P2G power station for heating. If wind curtailment still exists, it will be supplied by electric boilers. When wind curtailment has been fully absorbed, the unmet heat load will finally be supplied by CHP units. In Scenario 3, when the electrical and thermal output of CHP units are both reduced, the gas purchase cost and actual carbon emissions of the units are also reduced. This result verifies that considering P2G and its heat recovery can improve the wind power consumption rate of the system and reduce the unit operating cost and carbon emissions. Figure 7 shows the wind discard characteristics in six scenarios. Compared with Scenarios 1, 2 and 3, Scenarios 4, 5 and 6 add carbon capture devices, and the output proportion of 39-bus coal-fired units increases. In Scenario 4, when wind curtailment exists in the system, coal-fired units at bus 39 will not operate because the power output of wind power and CHP has already met the power load requirements. Therefore, the carbon capture power output is zero and no more wind power can be absorbed. In the period without wind abandonment, carbon capture devices can capture a large amount of CO2 to reduce carbon trading costs, but limited by storage capacity, the CO2 that cannot be stored needs to be re-emitted into the atmosphere.