Analysis of battery current microcycles in autonomous renewable energy systems

Battery currents in autonomous renewable energy systems (RES) are generally predicted or measured in terms of mean values over intervals of 1 min or longer. As a result, battery charge-discharge cycles with periods less than the averaging period are ignored, and the actual battery ampere hour (A h) throughput and resulting battery wear may be seriously underestimated, leading to optimistic prediction of battery lifetime. This paper considers short charge-discharge cycles or microcycles, arising from the characteristics of autonomous renewable energy systems, including generators, regulators, loads, and load inverter. Simulation results are used to show that inverters operating directly from the battery can cause microcycles, resulting in significantly increased battery throughput. Initial experimental results of the effects of microcycles on battery capacity and charging characteristics, and the contributing processes, are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.