This report describes development of an effort to assess Battery Energy Storage System (BESS) performance that the U. Department of Energy (DOE) Federal Energy Management Program (FEMP) and others can employ to evaluate performance of deployed BESS or solar photovoltaic (PV). To support consistent characterization of energy storage system (ESS) performance and functionality, EPRI—in concert with numerous utilities, ESS suppliers, integrators, and research organizations participating in the Energy Storage Integration Council (ESIC)—has developed a reference test manual. The. Fundamentally, energy storage (ES) technologies shift the availability of electrical energy through time and provide increased flexibility to grid operators. The certification approach.