Digital Twin Modeling and Validation of a Gravity Energy Storage System Using Opal-RT

This paper presents the development and validation of a digital twin for a gravity energy storage system that repurposed idle oil wells for long-duration, low-cost, and sustainable energy storage. The system was initially modeled in MATLAB/Simulink and subsequently implemented in the Opal-RT real-time simulation environment. To meet a 50 ..mu..s time step for real-time execution, the model was modularized into three functional subsystems, namely, electrical, mechanical, and well dynamics, each deployed on separate processor cores to enable parallel computation. Validation of the digital twin was conducted by comparing Opal-RT simulation results against measurements from a prototype device for one round trip. The real-time simulation replicated the system's performance, achieving an R2 of 94.59% and a root-mean-square error of 3.65% for grid power during discharging. Notable differences exist during the charging operation, requiring additional diagnosis and root cause analysis. Motor torque demonstrated good agreement with R2, exceeding 99.9%, and with the root-mean-square error below 0.55 Nm. These results confirm the ability of the digital twin models to mimic real-time performance and identify system-level opportunities for performance improvements and optimization of round-trip efficiency.