Active surface area approximation in a lead-acid cell for optimal performance in renewable energy systems

Abstract

In a renewable energy system, lead-acid batteries are required to last as long as possible whilst providing deep discharges and are usually charged in an intermittent manner. This type of operation is severely detrimental to the electrodes and optimal performance cannot be guaranteed. Correct operation can be achieved if a charge controller receives accurate information about the state of the battery and its cells. Accurate approximation of the available active surface area is essential to optimal performance since it determines the overall capacity and reaction rates of various secondary processes. This paper improves on the current understanding of the active surface area in a lead-acid cell during discharge by comparing three approximation methods. Two methods use the state-of-charge based on porosity whilst the other method uses the charge per unit volume to determine the remaining capacity. These three methods are used in a comprehensive macro-homogeneous electrochemical model which accounts for initial temperature differences. Reported experimental behaviour is used to evaluate each method and recommendations are made regarding the selection of associated parameter values. The approximation method by Cugnet et al. (2009) is the most suitable because it always results in a concave morphology. The current work can aid in the development of a health-conscious battery management system