The integration of energy storage system caters to the stable operation of power grids with high renewable energy penetration. The battery energy storage systems (BESS) in Grid Support Mode (GSM) provides functionalities of Grid Stabilization, Frequency and Voltage Regulation, Load Levelling, Peak Shaving and Power Quality Constraints. This paper provides the detailed evaluation on integrating 5.5 MW/10MWh battery energy storage system with AEW Energie AG as an independent electricity company, located in the North of Switzerland. The primary frequency control function of BESS has been tested using DIgSILENT Power Factory simulation environment and measured operational data from the commissioned site. AEW utilizes the Battery Energy Storage System (BESS) initially as a learning platform to enhance grid stability and add more distributed energy resources (DERs) to their operations. Longer term, there are plans to identify capabilities that can address new market opportunities, including, virtual power plants, and energy trading.