## 3 Results and Discussion
### Hourly Energy Balance for the Selected Integrated System  
The previous analysis demonstrates that the mixed operating strategy guarantees the best techno-economic performance for the investigated integrated energy system. To evaluate in more detail the behaviour of the geothermal-driven CHP apparatus, Figure 11 depicts the distribution of hourly global electric efficiency and _EUF_ index adopting mixed operations. The electric effectiveness ranges between 7.7% and 16.3%. As already observed, the maximum electric efficiency refers to full load operation with the sole electric production (Figure 6). It is worth noting that a concentration of high electric and low _EUF_ points is registered during the hot season due to the low thermal request during this period. In this case, most of the geothermal source is used for electric production at high electric load, with good electric efficiency and low thermal performance. Furthermore, in order to guarantee the complete exploitation of the geothermal source, the integrated unit produces the sole electric energy at full load when the thermal request is absent. Figure 12 shows the hourly energy balances in typical winter and spring days (3 January and 3 April). The CHP unit is capable of fulfilling the thermal load almost completely in January and a negligible integration is needed at 7:00 h (0.5% of the daily energy demand), whereas no thermal surplus is registered. A slightly higher integration is necessary in April (3.7% of the daily demand) due to the thermal request at 15:00 h, lower than the minimum thermal power of the combined apparatus. As far as the electric production is concerned, a very high self-consumption is guaranteed for both reference days (89.3% and 96.2% in January and April, respectively) and integration is required during  
Figure 10: Influence of the operating strategy on the economic viability of the integrated energy systems. the daytime, when the thermal request is present. Conversely, when there is no thermal demand, the whole geothermal source is used to produce electric energy. In this case, a higher electric surplus to be injected to the grid is noticed (39.1% in January and 47.6% in April). The thermal demand decreases noticeably during the hot season (Figure 13) and it is present for a few hours per day. The thermal self-consumption is always higher than 94% and the system works at full load for 21 h in July, satisfying almost completely the daily electric request (values higher than 99% are found). The electric energy injected to the grid is 62.6% and 49.2% of the daily production in July and October, respectively. Figure 11: Hourly electric efficiency (**a**) and energy utilisation factor (**b**) for the integrated geothermal energy system. Mixed strategy. Figure 12: Hourly thermal and electric balance of the integrated energy system unit in January (**a**,**c**) and April (**b**,**d**) typical days. Mixed strategy. Table 4 summarises the yearly techno-economic performance of the integrated geothermal CHP system with mixed operation strategy. The global electric efficiency is equal to 13.4% and confirms that the parallel transcritical configuration guarantees high performance in line with medium and large-scale geothermal CHP systems [57]. The energy utilisation factor reaches 19.2% while the marginal efficiency of electric production is 14.4%.