Abstract

This work focuses on Cold Thermal Energy Storage (CTES), a technology that has attracted growing interest in recent years and represents a key element for achieving the European decarbonisation targets. Among the available technologies, Phase Change Materials (PCMs) represent a promising solution due to their high energy density; however, their widespread adoption remains limited by slow solidification kinetics and the formation of an insulating solid layer around the heat exchanger, which significantly increases the charging time.

This work addresses these limitations through a combined experimental and numerical investigation on SP9 GEL, a low-temperature PCM supplied by Rubitherm. A five-month laboratory campaign was carried out at the Process and Energy Laboratory of Delft University of Technology to identify an effective and rapid solidification strategy.

Based on the experimental outcomes, the PCM was integrated into the existing 4th-generation district heating and cooling (4GDHC) network of the “Grande Sud” shopping mall in Naples, Italy.

A dynamic simulation in TRNSYS 18 was performed to evaluate the performance of CTES under realistic operating conditions during a representative summer day.

Despite the partial stratification caused by the large tank height, the PCM tank allowed the complete shutdown of the heat pumps for approximately four hours in the afternoon. On the same day, 72.39% of the photovoltaic surplus was stored as thermal energy instead of being exported to the grid, confirming the effectiveness of the Power-to-Thermal (P2T) strategy under high solar availability.

These findings show that cold thermal storage can serve as an effective reservoir for surplus electricity generated by non-dispatchable renewable energy sources. However, realising this potential requires careful consideration of the operating conditions, the selection of a PCM suited to the target application, and a tank design capable of exploiting the entire available storage volume.