## 3 Results
### Coupled Generation of Electricity and Heat with or without Waste Heat Integration  
In Figure 10, the round trip utilization (RTU) is plotted against the round trip efficiency (RTE) for the coupled generation of electricity and heat without waste heat integration. Each marker represents a physically feasible concept. Lighter markers represent the lower compressor discharge temperature (CDT) of 450 \({}^{\circ}\)C, while darker ones represent a CDT of 625 \({}^{\circ}\)C. Red-bordered markers represent concepts using CO\({}_{2}\) as the working fluid, while green-bordered ones represent concepts using Argon. Diamonds represent concepts with a recuperator in the charge cycle. The star-shaped markers represent the results for open concepts. Values for RTU of up to 87% are calculated, albeit at the expense of RTE, which all remain below 25%. Regarding open cycles, it should be noted that only very few concepts are physically feasible, and they show very low values for both RTU and RTE. While the use of different working fluids in the closed concepts also does not show clear trends, the use of a recuperator in the charge cycle allows for concepts with CDT = 450 \({}^{\circ}\)C; without a recuperator, concepts with a lower compressor discharge temperature are not feasible. The following figures depict the results for RTU over the pressure ratio (\(\Pi\)) of the compressor in the charging cycle: Figure 11 covers the full pressure ratio range, while Figure 12 is limited to 0 to 10. Most concepts have pressure ratios up to 10 and slightly above. The exception is the open concepts, where the required pressures are significantly higher, with achievable values for RTU being low, as mentioned earlier. In closed concepts, it is noticeable that the working fluid argon enables lower pressure ratios. Figure 10: Coupled generation of electricity and heat without waste heat integration: RTU over RTE. As lead concepts for coupled generation of electricity and heat without waste heat integration, those defined with the highest RTU for CDT = 450 \({}^{\circ}\)C and CDT = 625 \({}^{\circ}\)C are chosen, while keeping the systems as simple as possible. If similar RTU values are obtained, the simpler system is selected, as shown in Figure 10:  
* CHP1: Working fluid is air. Process heat extraction before the turbine in the discharge line. Recuperator in the charge line. \(\vartheta_{\text{max}}\) = 450 \({}^{\circ}\)C; RTU = 86.8%; RTE = 10.3%; \(\Pi\) = 8.1. Flowchart: Figure 13.
* CHP2: Working fluid is air. Process heat extraction after the compressor in the discharge line. \(\vartheta_{\text{max}}\) = 625 \({}^{\circ}\)C; RTU = 81.2%; RTE = 19.0%; \(\Pi\) = 2.0. Flowchart: Figure 14.  
Figure 11: Coupled generation of electricity and heat without waste heat integration: RTU over \(\Pi\) (complete solution area). Figure 12: Coupled generation of electricity and heat without waste heat integration: RTU over \(\Pi\) (restricted solution area). In Figures 15-17, the results for concepts with additional waste heat integration are depicted. The square markers represent concepts with a recuperator in both the charge and discharge lines. Figure 14: Lead concept CHP2 for coupled generation of electricity and heat without waste heat integration. Figure 13: Lead concept CHP1 for coupled generation of electricity and heat without waste heat integration. Figure 16: Coupled generation of electricity and heat with waste heat integration: RTU over \(\Pi\) (complete solution area). Figure 17: Coupled generation of electricity and heat with waste heat integration: RTU over \(\Pi\) (restricted solution area). Figure 10:0 Coupled generation of electricity and heat with waste heat integration: RTU over RTE. The integration of waste heat leads to higher RTU values, reaching nearly above 100%. As lead concepts for the coupled generation of electricity and heat with waste heat integration, the following are defined, as shown in Figure 10:1  
* CHP+WHI1: Working fluid is air. Process heat extraction before the turbine in the discharge line.