The economic end of life of electrochemical energy storage

The useful life of electrochemical energy storage (EES) is a critical factor to system planning, operation, and economic assessment. Today, systems commonly assume a physical end -of -life criterion: EES systems are retired when their remaining capacity reaches a threshold below which the EES is of little use because of insufficient capacity and efficiency. We have found, however, that there are some instances where, while the EES is still functional, it is no longer economically profitable; we call this criterion the economic end of life of the system. This criterion depends on the use case and degradation characteristics of the EES. Using an intertemporal op- erational framework to consider functionality and profitability degradation, our case study shows that the economic end of life could occur significantly faster than the physical end of life. We argue that both criteria should be applied in EES system planning and assessment. We also analyze how R&D efforts should consider cycling capability and calendar degradation rate when considering the economic end of life of EES.