Technical assessment of phase change material thermal expansion for passive solar tracking in residential thermal energy storage applications

Phase changing materials (PCMs) have been widely investigated for Latent Heat Thermal Energy Storage (LHTES) applications in the last decades, due to their inherently high volumetric storage density and thermal control features. Nonetheless, PCMs and their related LHTES systems still require significant scientific and technical advancements and more efficient market penetration strategies, to be able to play a key role in the massive transition towards renewable energy that is expected to take place in EU in the near future. Some of the most investigated PCMs for low to medium temperature LHTES belong to the alkanes/paraffins family, which is characterized by a relatively high volumetric expansion solid-to-liquid phase transition. This is generally considered a side effect, which should be accounted for to avoid damaging the containment structure. However, it could also represent an opportunity to add extra functionalities and increase the overall efficiency of LHTES systems. In this paper, we evaluate the feasibility of using the mechanical work generated by the volumetric expansion cycles in a paraffin-based LHTES device for photovoltaic (PV) solar tracking purposes, thus assuming a novel paradigm for the efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical approach. Accurate charge/discharge profiles of the TES are implemented, considering data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this analysis allow to estimate the tracking capability of the chosen PCM in terms of number/surface of actuated PV panels.