## 4 Concluding Remarks  
This study evaluated the energy transfer quality from a residual heat source to a working fluid in an ORC, using a shell-and-tube TES unit as the benchmark configuration, with the aim of identifying the key factors that influence thermal and exergetic efficiencies. The results indicate that both efficiencies increase as boiler temperatures approach the critical point of the working fluid.  
In particular, for the direct-heated ORC, thermal efficiency was primarily influenced by the temperature difference between the boiler and the heat source, achieving a maximum value of approximately 50%.  
The integration of a TES system with an optimized temperature profile significantly improved the exergetic efficiency. Two extreme configurations were evaluated: one replicating the thermal source profile and the other mimicking the isobaric heating profile  
Figure 8: Exergetic and sizing key parameters of the ORC-TES system for the three pinch-point temperatures, in crimson, green, and blue, respectively, are at 5, 10, and 15 \({}^{\circ}\)C. (**a**) Exergetic efficiencies. (**b**) Volumetric flows. (**c**) Pipeline diameters.  
of the working fluid. The latter demonstrated superior performance, reaching exergetic efficiencies of nearly 90%. Interestingly, the pinch-point temperature showed a negligible impact on the system's thermal efficiency.  
Additionally, all tested thermal oils presented similar mass and volumetric flow rates, internal velocities, and required pipe diameters, aligning well with commercially available tubing (6.35 mm). Among them, Thermal Oil 2 exhibited the most favorable behavior due to its thermal stability and minimal variation in thermophysical properties under operating conditions. These findings suggest that system configuration and operating conditions are more decisive for performance than the specific choice of thermal oil, as key design parameters remained consistent across all fluids tested.  
Conceptualization, A.B. and J.G.; methodology, J.G., A.B. and H.Q.-L.; validation, A.B. and J.R.; formal analysis, J.G., N.S., A.B. and J.R.; investigation, A.B., J.R. and N.S.; resources, J.G. and H.Q.-L; writing-original draft preparation, A.B., J.G. and H.Q.-L.; writing-review and editing, J.G. and H.Q.-L.; visualization, J.G. and H.Q.-L.; supervision, J.G. and H.Q.-L.; project administration, A.B.; funding acquisition, J.G. and H.Q.-L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by The National Fund for Scientific and Technological Development (FONDECYT), Chile under the grant numbers 11250144 and 1240765.  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
[PERSON] gratefully acknowledges the support provided by the Guillermo Blanco Scholarship from the Universidad de Talca, Chile. [PERSON] and H.Q.-L. acknowledge funding from the National Fund for Scientific and Technological Development (FONDECYT), Chile, under Grant Nos. 11250144 and 1240765.  
The authors declare no conflicts of interes.  
The following abbreviations are used in this manuscript:  
C1 Configuration 1 C2 Configuration 2 GHG Greenhouse gases GWP Global Warming Potential HTF Heat Transfer Fluid PTC Parabolic Trough Collector ORC Organic Rankine cycle TES Thermal Energy Storage WF Working Fluid