Numerical Analysis on the State of Charge of an Ultra-High Temperature Latent Heat Thermal Energy Storage System

Ultra-high temperature thermal energy storage (UHTES) and conversion is an emerging field of technology that enables much higher energy densities (>1 MWth) and conversion efficiencies than conventional thermal energy storage technologies. Our research group of Solar Energy Institute is currently developing a novel latent heat thermophotovoltaic (LHTPV) battery that utilizes Si-based alloys to store either surplus renewable electricity or concentrated sunlight in the form of latent heat at temperatures close to 1200 ºC and convert it back to electricity on demand. Determining the State of Charge (SoC) of this ultra-high temperature thermal battery is imperative to regulate its real-time operation and optimize its performance. However, using of several sensors within the storage system –as mainly done in low temperature phase change materials (PCMs) to quantify their SoC - becomes costly and challenging for this range of operating conditions. This study presents a numerical method, which is used to get an understanding of the physical processes taking place during the LHTPV operation and capture comprehensive data of time varying flow variables that can be difficult to record during real-time operation. Our results indicate that we can describe the system’s SoC by measuring the time-varying temperature at its sidewalls and the input/output heat flux values, without the need of knowing beforehand the thermophysical properties of the used materials. Based on these variables we can define several indicators that can help us obtain a better understanding of the required physical signals to be measured in order to determine its SoC, during real-time operation.