Lessons learned from operating a large-scale battery storage system – challenges and improvements

Large-scale battery energy storage systems (BESS) are increasingly used for various applications, including ancillary services. Our 5MW/7.5MWh hybrid research BESS M5BAT consists of ten battery units with two lead-acid and three lithium-ion technologies and operates mainly in the frequency containment reserve (FCR) market. This study presents experiences, challenges, and solutions for the successful operation of M5BAT in field application. Results indicate that 75% of outages are caused by communication and sensor errors, as well as balancing and SOC estimation issues. Balancing issues reduce usable capacity by up to 35% of a M5BAT battery unit. Therefore, solutions from manufacturers and intelligent energy management systems that detect issues early and trigger maintenance cycles, must be implemented. Low partial load operation (<10% utilization) increases losses in the power conversion system, resulting in round-trip efficiencies of 70% to 75%. Implementing an efficient inverter control algorithm including inverter switching rules and the introduction of multi-use operation to increase utilization helps enhancing efficiency. At M5BAT, we achieved around 80% round-trip efficiency in FCR operation and about 85% in energy trading operation. Our findings provide a valuable foundation for future research aimed at improving large-scale BESS design and operation, contributing to sustainable energy solutions’ widespread adoption.