CIMA+ was hired by PCL Constructors Canada Inc. as a consultant for their client Canadian Solar Solutions Inc. as they completed the design and construction of the Battery Energy Storage System (BESS). The project, delivered in EPC mode (engineering, procurement and construction), consists of two 2 MW inverters and 68 battery racks interconnected to Hydro Ottawa’s Ellwood substation and has a total system capacity of 4 MW/2.76 MWh. This first utility scale energy storage system in the region is controlled by the Independent Electricity System Operator (IESO), in order to support grid demand response requests. The main challenges consisted of completing a design started by another firm, integrating a different battery technology within an existing building, reducing the DC fault currents to levels that commercially available components can support, and integrating a high-performance HVAC system.