Analytical analysis of stationary Li-Ion-battery storage-system efficiency on a large scale

In recent decades, Li-ion battery (LIB) technology has matured and is now the dominant battery technology for many mobile applications. Building on that success, LIBs are increasingly being adopted for stationary applications, as well. The Energy Information Administration (EIA) datasets show a huge increase in LIBs' use in the country, providing an opportunity to quantify their real-world performance. In this study, the reported efficiency of stationary LIBs units in storage plants in the USA is analyzed using the energy storage plants' data available in the EIA datasets. The plants are categorized according to the initial operating year; each group's efficiency is modeled as a function of the number of cycles/ month. We found that 1) newer plants show higher efficiencies, 2) the efficiency typically increases with the LIBs' number of cycles/month, 3) the efficiencies are between 80-90 % for those that cycled more than five times in a month, 4) The combined efficiencies of battery and power electronics are observed to be 87-94%, and 5) the degradation of the efficiency is imperceptible from these data, even for the systems that have been operating for > 5 years. Finally, we discuss possible reasons for the lower reported efficiencies for those systems that cycle infrequently.