Examination of VRLA battery cells sampled from the Metlakatla battery energy storage system

One of the principal concerns when a battery energy storage system (BESS) is being considered for utility applications is the ability of the battery to provide the anticipated lifetime on which the project was justified. The reason for this is that the battery is a significant cost element in the overall system; and, in the past, the batteries deployed have not been fully able to demonstrate their projected lifetime in these applications. Even though most of the past demonstrations have utilized flooded lead-acid technology which was considered to be matured, unexpected failure modes were often cited for the reduced lifetime of the battery. Valve-regulated lead-acid (VRLA) batteries are becoming more widely utilized and are displacing flooded lead-acid technology in applications ranging from typical standby usage such as emergency lighting, telecommunications backup and uninterruptible power supply (UPS) to more cyclic usage in photovoltaics and other renewable energy systems and even in electric vehicles. Hence, there is a high probability that future BESS projects will utilize VRLA technology. The purpose of this paper is to discuss the surveillance studies conducted by GNB and Sandia National Laboratories on VRLA cells in a BESS installation to assess their progress, after almost three years of operation, in meeting their projected lifetime.