## 3 Thermodynamic Behavior of the ORC-TER System  
To elucidate the performance enhancement introduced by the integration of an intermediate energy accumulator based on thermal oil, a direct-heated ORC configuration is employed as a benchmark. Figure 3 presents the thermal and exergetic efficiencies for the three evaluated scenarios: the two TES configurations (C1 and C2) and the direct thermal source case, each assessed as a function of the boiler saturation temperature. The thermal efficiency, \(\eta_{1}\), as depicted in Figure 3a, demonstrates no sensitivity to the inclusion of a TES system. This outcome is consistent with the thermodynamic expectation that the mode of heat delivery to the boiler does not influence the first-law performance of the cycle. Furthermore, a positive correlation between boiler saturation temperature and thermal efficiency was observed, reflecting the classical behavior of Rankine-based systems. Notwithstanding these trends, the selection of operational parameters must account for critical system constraints, including the need to avoid proximity to the working fluid critical point [68], to operate below the maximum allowable pressure of construction materials, and to ensure a sufficiently high vapor quality at the turbine outlet [14] to mitigate the risk of mechanical degradation. Furthermore, Figure 3b illustrates the exergetic efficiency of both TES configurations at a fixed pinch temperature of 10 \({}^{\circ}\)C concerning the working fluid, compared to the direct-heated benchmark, depicted in black. C2 exhibits a markedly higher exergetic efficiency than C1. This result highlights the importance of aligning the thermal oil temperature with the working fluid profile, maintaining proximity to the system's saturation temperature while preserving the specified pinch temperature difference. From a design perspective, this alignment enables more effective utilization of the available thermal potential, reduces irreversibilities in the heat transfer process, and maximizes the quality of the delivered energy. As illustrated in Figure 3b, the improvement in heat delivery quality is substantial when thermal oil is employed to indirectly preheat the working fluid. Consequently, it is essential to evaluate the influence of thermal oil properties and pinch-point temperature on this effect. Figure 4 presents the average relative percentage difference in exergetic efficiency for the three thermal oils analyzed. In C1, shown in Figure 4a, exergetic efficiency decreases at low pinch-point temperatures and exhibits only a slight improvement as the pinch-point increases, with minimal variation across the different oils. Conversely, C2, shown in Figure 4b, demonstrates a pronounced increase in exergetic efficiency at low pinch-point temperatures, reaching up to a twofold improvement. These findings indicate that C2, combined with a low pinch-point temperature, yields superior performance. Nevertheless, the pinch-point must be sufficiently high to ensure adequate heat transfer, depending on the heat exchanger design. The characteristics of the system impose constraints on the working fluid flow rate, while turbine specifications define the flow demands and the mechanical output. Equipment design and dimensions are also established based on these parameters. Figure 5a illustrates the mass flow rate, whereas Figure 5b presents the volumetric flow rate. Although volumetric flow is the primary variable for equipment sizing and scaling, the mass flow exhibits a distinct minimum near 80 \({}^{\circ}\)C. This trend provides a practical guideline for  
Figure 4: Average relative percentage difference in exergetic efficiency for the three thermal oils evaluated, across varying pinch-point temperatures, in configurations (**a**) C1 and (**b**) C2. In both figures, crimson represents Therminol LT, blue corresponds to Parather HR, and yellow denotes Paratherm NF. Figure 3: Basic thermodynamic analysis of the ORC-TES system.