Lithium-ion Battery Degradation Assessment in Microgrids

Lithium-ion-based Battery Energy Storage System (BESS) play an important role in solving power supply problems in micro-grids due to their performance characteristics such as high power, high efficiency, low self-discharge, and long lifespan. Therefore, is essential to know the BESS useful life, especially by understanding how its degradation process evolves over time. In this context, this article presents a methodology capable of analyzing the degradation process of the BESS Li-ion batteries when used into a micro-grid. Since BESS degradation is a consequence of how the battery cells are operated (e.g.; initial and final state-of-charge (SOC) values within each cycle), we propose the use of a technique capable of estimating an equivalent degradation factor regardless of their operation. To assess BESS degradation, an economic dispatch is carried out, which incorporates the use of a BESS inside a micro-grid. The economic dispatch is formulated as a MILP optimization problem that allows the BESS to supply the electricity demand during an eighthour period of energy autonomy per day. Results show a useful life of2233 cycles of usage of the BESS. Thus, if the BESS works under the proposed conditions, its lifespan will be over 7-years approximately. In this case, it is demonstrated that the BESS operates under high SOC ranges, (100-0%), (90-0%) and (SO-0%), inferring that in each cycle almost all the available stored energy is consumed.