As the use cases for battery energy storage systems (BESS) evolve, so does the way the batteries are operated. How these changes affect BESS lifetime and reliability is a question the industry needs answered, and one the International Energy Agency’s Photovoltaic Power Systems Programme (IEA-PVPS) is working to address. Erik Marstein, director of Norwegian PV Research Center FME Solar, outlines the results of recent research into BESS reliability and how asset owners can take system aging into account in daily operations.