# Optimal Configuration of Integrated Energy System Based on Energy-Conversion Interface
## 4 Case Analysis
### Economic Analysis  
It can be seen from Table 1 that from the obtained device-configuration result from the minimum comprehensive system cost, a gas turbine with higher power-generation efficiency was selected and installed. For the electricity-gas conversion device, energy consumption exists in the process of electric-energy conversion, and gas supply was sufficient in this paper, so it was not installed. The gas boiler was not installed, either, due to the existence of a highly efficient electric-heat pump. The remaining devices were installed because of their own advantages. For example, the input energy of absorption refrigeration and the waste-heat boiler is the residual smoke of the device with lower cost, which can improve the efficiency of the entire energy-production device; electric refrigerators and electric-heat pumps have the characteristic of high energy-conversion efficiency. The maximum output level of each device in different months of the year is shown in Figure 10. Figure 11 shows the annual energy-flow output of each device in the energy-conversion interface. The coupling of various energy forms can also be seen in Figure 11. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Aims**} & \multicolumn{10}{c}{**Number of Installed Devices**} & \multicolumn{10}{c}{**Target Value**} \\ \cline{2-13}  & **GT** & **ICE** & **P2G** & **WB** & **HP** & **GB** & **EC** & **AC** & **ES** & **TS** & **CS** & **C (Ten Thousand** & **\(\mathbf{\eta_{eu}}\)** \\ \hline
**Economy** & 1(4\#) & 0 & 0 & 7 & 2 & 0 & 2 & 4 & 309 & 62 & 67 & 4385.18 & 0.853 \\  & 0 & 0 & 0 & 0 & 6 & 0 & 15 & 0 & 0 & 0 & 0 & 5560.28 & 1.564 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Number of installed devices under different objective functions. Figure 10: Device output level and unit adjustment: (**a**) electric refrigerator; (**b**) electric-heat pump; (**c**) absorption chiller; (**d**) waste-heat boiler. Figure 12 shows the output of the device with daily running power conservation, and gives the graphs (Figure 13) of electricity conservation on the typical days of January, July, and October. The electric-load supply consists of power-grid purchase, gas-turbine power generation, and electric-energy storage discharge. In addition to electric-load supply, there are two power-flow directions of electricity storage and electricity sales. As shown from the above figures, the overall system energy flow satisfies the conservation of electrical energy. In the month when electric load was relatively low, gas-turbine power generation mainly met the load demand, and electricity was sold at the peak of the electricity price. In the month when electric load was high, purchased electricity in the system was large, so there were no electricity  
Figure 11: Annual energy-flow output of each device in the system. Figure 12: Output situation of daily running power-conservation device. Figure 13: Device output with constant current on a typical season: (**a**) January; (**b**) July; (**c**) October. sales. It can be seen from the device output of the typical season that electric-load supply mainly came from grid-power supply and gas-turbine power generation. In the low-price stage of electricity, a small amount of energy storage occurred due to a lower energy cost. In the peak stage of electricity price, due to the high cost of electricity, the energy storage device will release the energy and sell the remaining electricity generated by the gas turbine online, thereby improving the economy of the system. Figure 14 shows the output of the device with daily heat-energy conservation, and gives the heat-energy conservation map for three seasons. Heat-load supply consists of a waste-heat boiler and an electric-heat pump. In addition to heat-load supply, there is thermal-energy storage. As can be seen from Figure 14, the whole system satisfies the conservation of thermal energy.