Thermal Design and Analysis of a Solid-State Grid-Tied Thermal Energy Storage for Hybrid Compressed Air Energy Storage Systems

Power overgeneration by renewable sources combined with less dispatchabe conventional power plants introduce the power grid to a new challenge, i.e., instability. The stability of the power grid requires constant balance between generation and demand. A well-known solution to power overgeneration is grid-scale energy storage. Although different energy storage technologies have been tested and demonstrated, reducing the cost of energy storage remains as a challenging goal for researchers, industries, and governments. Compressed Air Energy Storage (CAES) has been utilized for grid-scale energy storage for a few decades. However, conventional diabatic CAES systems are difficult and expensive to construct and maintain due to their high pressure operating condition. Hybrid Compressed Air Energy Storage (HCAES) systems are introduced as a new variant of old CAES technology to reduce the cost of energy storage using compressed air. The HCAES system split the received power from the grid into two subsystems. A portion of the power is used to compress air, as done in conventional CAES systems. The rest of the electric power is converted to heat in a high-temperature Thermal Energy Storage (TES) component using Joule heating. In this study, a solid-state grid-tied TES system is designed to operate with a HCAES system. The storage medium is considered to be high-temperature refractory concrete. The thermal energy is generated inside the concrete block using resistive heaters (wires) that are buried inside a concrete block. A computational approach was adopted to investigate the performance of the proposed TES system during a full charge/storage/discharge cycle. It was shown that the proposed design can be used to receive 200 kW of power from the grid for 6 hours without overheating the resistive heaters. The discharge computations show that the proposed geometry of the TES, along with a control strategy for the flow rate can provide a 74-kW micro-turbine of the HCAES with the minimum required temperature, i.e., 1144K at 0.6 kg/s of air flow rate for 6 hours. The computations were performed in ANSYS/FLUENT and the results were verified and validated using a grid independence study.