Grid-Connected All-Iron Redox Flow Batteries for Long-Term Energy Storage: Field Operation and Digital Twin Integration

The increasing penetration of renewable energy sources presents challenges for power grid stability due to their intermittency. Long-term energy storage systems are critical for system security and optimizing operations. This paper presents an all-iron redox flow battery (RFB) energy storage system for grid-connected applications, including a field test in the Danish power system and the developing of a digital twin model to enhance system monitoring and operational capabilities. The proposed digital twin combines an equivalent circuit model (ECM) for the battery with an empirical model for the power conversion system, providing a comprehensive representation of the dynamic and steady-state performance of such real-world power system components. Data collected from the 75kW/500kWh all-iron RFB system are used for online modeling of steady-state and dynamic performance. Addressing the challenges of modeling industrial assets in the field application, our model achieved a near 1 R-squared value with a root mean square error (RMSE) below 2 kW for overall power response accuracy. For dynamic modeling, R-squared values of 0.42 and 0.22 were obtained for AC and DC power modeling with accurate behavior simulation. The demonstrated performance in real-time system behavior tracking and modeling highlights the potential of the proposed model for optimizing field operations and providing predictive insights.