Experimental characterization of a lab-scale cement based thermal energy storage system

Highlights: • We present a new modular cement based solid-liquid thermal energy storage concept. • A lab-scale prototype storage unit is characterized through dedicated experiments. • A heat balance model is developed to describe its energy storage characteristics. • The methodology can be scaled and applied to multi-unit storage systems. -- Abstract: In this study, a new modular cement based solid-liquid heat storage concept is presented. Advantages of this storage concept are its scalability, facilitated by a flexible modular construction, and its potential double purpose as heat storage and foundation structure. The storage system may be integrated in new as well as existing buildings, or be installed in the subsurface. A lab scale 1 m³ prototype storage unit was constructed, consisting of a helical heat exchanger embedded in a cement-based thermal filling material. Dedicated heat charging and discharging as well as heat loss experiments were performed at storage temperatures of 60 °C and 80 °C within a well-controlled laboratory environment in order to characterize the heat transfer processes and storage characteristics as well as the performance of the heat storage prototype. The maximum thermal capacity at 80 °C supply temperature is found to be 52 kWh/m³, with maximum charging/discharging rates of up to 8 kW and heat losses of 4.4 kWh/24 h at full capacity. Based on the found characteristics, a heat balance model is developed and parameterized. Simulated and experimental temperatures and heating rates are in very good agreement, which shows that the dominant heat transfer processes and material characteristics are well understood and quantified.