## 4 Case Studies
### Analysis of Simulation Results  
#### 4.2.1 Effects of P2G on Operation of Integrated Power-Natural Gas-Heating Energy Systems  
The optimal dispatch results are shown in Table 4. Wind power output and curtailed wind power without P2G and with P2G are given in Figures 4 and 5, respectively. The power output of coal-fired units and gas-fired units is shown in Figure 6. Besides, the linepack of pipelines and gas pressure of node 6 are given in Figures 7 and 8. Gas flow of gas wells and gas storage as well as volume of gas storage can be found in Figures 9-11. Figure 3: Hourly demand of power, gas and heating. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Unit No.** & \(\mathbf{\alpha/(10^{3}\text{lb/h})}\) & \(\mathbf{\beta/(1\text{lb/(MW\text{-}h)})}\) & \(\mathbf{\gamma/(1\text{lb/(MW^{2}\text{-}h)})}\) & \(\mathbf{\delta/(1\text{lb/h})}\) & \(\mathbf{\lambda/\text{MW^{-1}}}\) \\ \hline Coal-fired & \(0.103\) & \(-2.444\) & \(0.031\) & \(0.504\) & \(0.021\) \\ unit 1 & \(0.103\) & \(-2.444\) & \(0.031\) & \(0.504\) & \(0.021\) \\ unit 2 & \(0.103\) & \(-2.444\) & \(0.031\) & \(0.504\) & \(0.021\) \\ Coal-fired & \(0.3\) & \(-4.07\) & \(0.051\) & \(0.497\) & \(0.02\) \\ unit 3 & \(0.3\) & \(-4.07\) & \(0.051\) & \(0.497\) & \(0.02\) \\ Coal-fired & \(0.32\) & \(-3.813\) & \(0.034\) & \(0.497\) & \(0.02\) \\ unit 5 & \(0.103\) & \(-3.902\) & \(0.015\) & \(0.163\) & \(0.02\) \\ Gain-fired & \(0.11\) & \(-3.902\) & \(0.016\) & \(0.172\) & \(0.021\) \\ unit 2 & \(0.11\) & \(-3.902\) & \(0.016\) & \(0.172\) & \(0.021\) \\ Gas-fired & \(0.11\) & \(-3.902\) & \(0.016\) & \(0.172\) & \(0.021\) \\ unit 3 & \(0.11\) & \(-3.902\) & \(0.016\) & \(0.172\) & \(0.021\) \\ \hline \end{tabular}
\end{table} 
Table 2: Emissions coefficient of thermal units in power systems. From these obtained results, when P2G is considered, it has obvious advantages in many aspects which can be described in details as below. 1. The total operational cost declined by $7000 and SO\({}_{\text{x}}\) emissions decreased by 790 kg. The main reasons for the decrease in operational cost are the injection of gas produced by P2G to gas network and thus the reduction of gas from gas wells. The main reason for the reduction of SO\({}_{\text{x}}\) emissions is the decrease of power output of coal-fired units. More specifically, the power output of coal-fired units is increased by 25.895 MW at 20:00 but decreased by 39.938 MW and 9.760 MW at 19:00 and 21:00, respectively. In general, the power output of coal-fired units is declined when P2G is taken into account and thus SO\({}_{\text{x}}\) emissions are decreased accordingly. 2. CO\({}_{2}\) is reduced by 620 ton due to the reduction of gas flow of gas wells and absorption of CO\({}_{2}\) by methanation process. 3. Wind power output is increased by 6266.742 MWh as well as the rate of wind power accommodation is raised from 74.42% to 95.78%. It is noted that increased wind power is converted to methane to be stored in natural gas network which can be used to supply peak gas load or heating load later. 4. As both gas load and heating load are peaked at 20:00, linepack is not sufficient at the time and gas pressure of gas node (for example node 6) may below its minimum pressure which will affect normal operation of natural gas network. In order to solve this problem, gas consumption for gas-fired units is decreased and accordingly power output of coal-fired units is also adjusted, which can be seen from Figure 6. Due to gas produced from P2G inflowing to natural gas network, linepack as well as node pressure are increased significantly which can be found from Figures 7 and 8. 5. Due to the increased gas from P2G to supply gas demand and heating demand, there has been a certain decline in the gas flow of gas wells and gas storage as well as an obvious increase in the volume of gas storage which can be seen from Figures 9-11.