Transient Thermofluids Analysis of a Ground-Level Integrated Diverse Energy Storage (GLIDES) System

In this work, a novel Ground-Level Integrated Diverse Energy Storage (GLIDES) system which can store energy via input of electricity or heat and deliver dispatchable electricity is presented [1]. The proposed system is low-cost and hybridizes compressed air and pumped-storage approaches that will allow for the off-peak storage of intermittent renewable energy for use during peak times. A detailed control-volume energy analysis of the system is carried out, yielding a set of coupled differential equations which are discretized using a finite difference scheme and used to model the transient response during charging and discharging. The energy analysis includes coupled heat transfer and pressure drop analysis used to predict system losses for more accurate round trip efficiency (RTE) calculations and specific energy density (ED) predictions. Preliminary analysis of the current prototype indicates an electric-to-electric RTE_E of 66% (corresponding to shaft-to-shaft mechanical RTE_M of 78%) and ED of 2.5 MJ/m³ of air, given initial air volume and pressure of 2 m³ and 70 bar. The electric power output ranges from a max of 2.5 kW to a min of 1.2 kW and the output current ranges from a max of approximately 21 amps to approximately 10 amps at 120 V, 60 Hz dispatchable electricity, over a period of approximately 50 minutes. Additionally, it is shown that heat transfer enhancement to the point of a 5-fold increase in air heat transfer rates results in a near 5% improvement in RTE_E (70% considering all component losses). Additional component efficiency improvements and efficiency gains due to system scale-up could see higher achievable RTEs.