Modellazione di un sistema di accumulo di energia termica a termoclino con 3 serpentine = Modelling of a thermocline thermal energy storage system equipped with 3 serpentines

Hybrid solar plants that combine concentrated solar power (CSP) and photovoltaic (PV) technologies require efficient thermal energy storage (TES) to ensure continuous and flexible operation. This work was carried out within the framework of an ongoing project supported by the Italian National Agency for New Technologies, Energy, and Sustainable Economic Development (ENEA). Thermocline single-tank systems are a promising solution because of their compactness and cost advantages, but their performance strongly depends on how effectively the thermocline can be maintained during charging and discharging. In this thesis, a computational fluid dynamics (CFD) model of a single-medium (molten salt) indirect thermocline TES with three internal serpentine coils is developed. The system is examined under different charging compositions: CSP-only, PV-only, balanced CSP–PV input, and simultaneous CSP–PV charging at high power. The results show that the time required to reach a target temperature varies across scenarios, yet the thermocline shape remains broadly similar in all cases, and its quality is not satisfactory. To improve thermal stratification, orifices were introduced inside the charging/discharging channel. Several parameters were investigated, including their position, radius, and number. The study finds that while the position of orifices has little impact, increasing the number of orifices and reducing their radius significantly enhances the sharpness of the thermocline and delays its degradation. Overall, the study highlights that while the composition of CSP and PV inputs mainly affects charging time rather than thermocline shape, the integration of channel orifices provides a practical and effective way to improve stratification quality. These findings offer valuable guidance for the design of advanced TES systems to support flexible operation in hybrid solar plants.