Optimal operational strategies for a retrofitted micro organic Rankine cycle coupled with a low temperature sensible heat thermal storage

The growing penetration of photovoltaic and solar thermal technologies in residential energy systems increases the need for effective flexibility solutions. In this context, thermal energy storage (TES) coupled with organic Rankine cycles (ORC) represents a promising option for small-scale thermally driven electricity generation and indirect energy storage, as encountered for instance in residential Carnot batteries or solar micro-cogeneration systems. However, existing studies analyse ORC performance under imposed or fixed heat-source conditions, thereby neglecting the transient interactions that arise when an ORC is directly coupled to a discharging TES. This study investigates the transient discharge operation of a sensible heat TES coupled to a retrofitted commercial micro-ORC ( μ ORC). The objective is to determine practical discharge strategies that maximise the total electrical energy recovered from the storage. A dynamic model of the coupled ORC–TES system is developed, calibrated against experimental data, and employed for operational optimisation. The results show that the most efficient discharge strategy combines an initial phase of moderate thermal stratification in the TES with a gradual reduction of storage temperature as discharge progresses. A simplified control strategy, in which the ORC heat-source mass flow rate and evaporator temperature glide are kept constant, achieve performance close to that of the fully optimised operation, with only a small reduction in total electrical energy output (1.8% for the investigated configuration). Experimental tests for the simplified control strategy confirm that the model captures the dominant ORC–TES interaction trends with sufficient accuracy for operational analysis. By explicitly addressing the coupled dynamics between TES and ORC during discharge, this work contributes to the definition of implementable operating strategies for ORC–TES systems. While the present study is restricted to the discharge phase, future work should focus on extending the methodology to the charging phase involving a coupled heat-pump–TES system, and on assessing discharge performance under alternative operating conditions, such as imposed power modulation, different discharge horizons, or externally constrained operation.