In the rapidly evolving landscape of energy storage, a groundbreaking study has emerged, offering a novel approach to modeling grid-connected battery energy storage systems (BESSs). Led by Mirko Ledro, an engineer at Ørsted Wind Power A/S and a researcher at the Technical University of Denmark, this research promises to revolutionize how operators optimize and utilize BESSs. The findings, published in the journal ‘Måling: Energi’ (Measurement: Energy), could have significant commercial impacts for the energy sector.
Traditionally, electrical models for BESSs are developed by suppliers or manufacturers through extensive laboratory testing of individual cells or modules. However, Ledro’s study explores a more practical and cost-effective method: modeling a BESS directly on-site using data from its energy management system (EMS) and battery management system (BMS). This approach eliminates the need to dismantle the BESS, making it a game-changer for operators seeking to maximize the potential of their existing infrastructure.
The research focuses on a 300kW/652kWh Nickel-Manganese-Cobalt (NMC) lithium-ion BESS, composed of ten racks, each equipped with a power converter system (PCS) and ten battery modules. By analyzing data from the EMS and BMS, Ledro and his team successfully characterized the electrical dynamics of the BESS using an equivalent Thevenin electric circuit. This circuit, composed of open circuit voltage, resistances, and capacitances, provides a comprehensive representation of the BESS’s behavior.
One of the key findings is the estimation of the BESS’s overall usable capacity and the efficiency of its PCS. “The usable energy capacity per rack is approximately 59.7kWh, which is about 91.5% of the rated DC energy capacity,” Ledro explains. This capacity is independent of the power at which the BESS is discharged, offering operators a reliable benchmark for planning and optimization.
Moreover, the study reveals that the PCS efficiency is above 94% when operating at 15% of the PCS rated power or higher, during both rectifier and inverter modes. This high efficiency is crucial for minimizing energy losses and maximizing the economic viability of BESSs.
The research also provides insights into the equivalent cell model, with the open circuit voltage and internal impedance expressed for the entire state-of-charge range. The total resistance and capacitance values are within expected ranges for NMC lithium-ion cells, validating the accuracy of the modeling approach.
So, how might this research shape future developments in the field? By demonstrating the feasibility of on-site modeling, Ledro’s study paves the way for more efficient and cost-effective optimization of BESSs. Operators can now leverage their existing data to fine-tune their systems, leading to improved performance and reduced downtime. This could accelerate the adoption of BESSs in the energy sector, supporting the transition to renewable energy sources.
Furthermore, the methodology developed in this study can be applied to other types of BESSs, expanding its potential impact. As the energy sector continues to evolve, innovative approaches like this will be crucial in driving progress and achieving sustainability goals. The findings, published in ‘Måling: Energi’, mark a significant step forward in the quest for optimal energy storage solutions.
