Analysis of battery lifetime extension in a SMES-battery hybrid energy storage system using a novel battery lifetime model

In off-grid wind energy systems, batteries often undergo frequent charge/discharge cycles, which reduce battery service life. In addition, due to motor start and other high 'inrush current' loads batteries undergo high rates of discharge which also degrade battery life. In this paper, a superconducting magnetic energy storage and battery hybrid energy storage system is proposed, which is beneficial in reducing battery short term power cycling and high discharge currents. To demonstrate system performance, a representative off-grid wind power system model is described in detail which incorporates turbulent wind variations, load variations and energy storage systems. To estimate battery lifetime improvement, a novel battery lifetime model is described, which quantifies the impact of both the number of charge/discharge cycles and also the effect rate of discharge. The model, is validated using previously reported data. This work advances previous studies by describing the estimated improvement in terms of battery life in a wind energy conversion application by use of superconducting energy storage and by presenting a novel method for doing so. In addition, the proposed battery lifetime model can be potentially used in other applications. (C) 2015 Elsevier Ltd. All rights reserved.