Feasibility of passive solar tracking through the thermal expansion of a PCM medium in a residential TES application: a numerical analysis

Phase Changing Materials (PCMs) are widely adopted and studied for Thermal Energy Storage (TES) applications, due to their inherent capability of storing and releasing high amounts of thermal energy in a narrow temperature range. At the same time, some of the materials commonly implemented in PCM-based TES devices (e.g. paraffin waxes or other organic materials) are known to experience a significant volumetric expansion (up to 20% or more) during their solid-to-liquid phase transition. Such expansion is generally considered a side effect, which should be accounted for to avoid damaging the PCM containment structure in the TES device. Recently, the thermally driven expansion of PCMs has been considered as a driving force for passive solar tracking, showing promising technical developments for dedicated solar tracking devices. In the present paper, we evaluate the feasibility of using the volumetric expansion cycles in a PCM-based TES device for PV solar tracking purposes, thus assuming an innovative and efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of the temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical implementation. Accurate charge and discharge profiles of the TES device are implemented, assuming data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this numerical analysis allow to perform a parametric study in terms of specific tracking capability of the chosen PCM (paraffin wax) vs. the installed PV modules surface.