## 3 Results and Discussion
### Influence of the Operating Strategy  
The yearly electric and thermal productions of the geothermal-driven CHP system were evaluated on an hourly basis considering the electric and thermal request of a commercial centre [112] Cited in the Phlegraean Fields area where geothermal sources at a temperature higher than 200 \({}^{\circ}\)C are present [77; 78]. The energy system can operate according to a thermal-driven, electric-driven, or mixed strategy. Depending on the energy request of the final user, a variable operation is registered all over the year. Figure 7 shows the comparison between the three operating strategies through the monthly energy balances of the CHP system. The electric demand presents a regular trend all over the year (around 44 MWh/month), while the thermal request variation is significant, ranging from 3.7 to 75.4 MWh/month (in August and January, respectively). The thermal-driven and mixed strategies show a similar behaviour. Both operating modes guarantee no thermal dumping and a significant self-consumption during the winter period, ranging from 89.0% to 100.0%. Furthermore, the thermal-driven strategy satisfies 100% of the user heat request during the summer, whereas mixed-mode ranges from 64.8% to 88.9% in the same months. On the contrary, the mixed strategy significantly increases the electric self-consumption to values always higher than 87.6%, while thermal strategy never satisfies the electric request (the maximum self-consumption is 69.1%). In this case, a significant integration is necessary during summertime (up to 90% of the electric load). The grid integration is present, although very small, when the mixed operation is adopted, despite the electric production always being larger than the energy demand. In fact, the electric and thermal loads are not simultaneous during the 24 h.  
The electric-driven operation produces very high electric self-consumption and moderate excess to be injected into the grid. Conversely, noticeable thermal dumping is registered. In fact, the electric-driven strategy forces a homogenous operation of the apparatus, with a mean electric load equal to 68.1% for all the year, owing to the continuous electric request. The system operates with intermediate electric performance and significant thermal production, as well as when the thermal demand is absent. Figure 6: Influence of the electric load on thermal power, electric power and geothermal flow at the entrance of ORC sub-system (**a**). Effect of the electric load on _EUF_, electric and marginal efficiency (**b**). On the contrary, the thermal-driven strategy guarantees a higher mean load (80.6%) with fewer operating hours (3692 h/year) because the thermal request is limited to the central hours of the day. This circumstance corresponds to lower equivalent operation hours (2977) as compared with the electric mode (6028). It is worthy to note that the mixed strategy reduces significantly the thermal dumping producing only electric energy at full load when the thermal request is absent. At the same time, the system operates in the high-performance range with 92.4% mean load and 8095 equivalent hours of operation. A slight excess of electric energy is noticed, due to the difference in the production and request timing. Figure 8 shows the annual balance for the three operating modes. The mixed strategy satisfies both thermal and electric demand with small integration (4.7% and 9.3% of the thermal and electric load, respectively) with 59.2% electric surplus and no thermal dumping. If the heat-driven mode is used, the integrated CHP apparatus is able to satisfy up to 95.7% of the thermal demand, while the electric self-consumption drops to 47.5%. Figure 7: Monthly electric and thermal balances for mixed (**a,b**) thermal- (**c,d**) and electric-driven (**e,f**) strategy. Furthermore, the economic viability of the integrated energy system was analysed and the different operating strategies were compared.