Modeling of Lead Acid Batteries in PV Systems

Abstract

The study of a photovoltaic system necessitates in a first time equivalent models of the main components such as PV generator model, storage element (batteries). The knowledge of their electrical characteristics remains a key factor in the simulation analysis. The battery behavior has been largely described in the literature by many authors such as Shepherd, Monegon, Mayer, Facinelli, Hyman, and CIEMAT. Most of the models require the knowledge of appropriate parameters. Batteries remain a complicated element, since they are the only dynamic element in a PV system. In fact many phenomenons can occur such as charge and discharge. Many parameters vary during theses processes: voltage, current, density, temperature, resistivity…etc. The selected model is that elaborated by CIEMAT. This model is general and normalized with battery capacity, it necessitate few input parameters, it takes into account the discharge, the charge and the overcharge processes, and can be applied for wide range of lead acide batteries used in PV systems. The CIEMAT (Copetti) model presents a good performance to represent dynamic and complex battery operation. This paper reviews this general lead acid batteries model and it agreement with experimental data obtained from tests with in photovoltaic systems. In order to validate these models, the behavior of different battery cycling currents has been simulated. Results obtained have been compared to real data in two PV systems, the first one with Varta Solar 100Ah-12V and the second one with Tudor 800 Ah-2V. For checking the validity of the mathematical model, the results of numerical simulation are compared with experimental data.