ABSTRACT
One of the major factors affecting PV batteries life-time is their operation in overcharge for extended periods. The purpose of this work is to present the results obtained after applying a new accelerated overcharge degradation procedure to two types of lead-acid batteries used in PV installations. This procedure has been developed in the frame of the QUALIBAT project (JOULE III). The following conditions hold for the overcharge test: Electrolyte temperature: 71°C; Overcharge: charge at constant voltage (floating voltage specified by the manufacturer); Length of the test: continuous periods of 12 days. After each period of 12 days the battery capacity is measured at 25°C. The degradation of the batteries has been evaluated through the capacity evolution along the overcharge tests. Other parameters useful in the characterization of the process, such as remaining passing current and electrolyte level during the tests, have also been studied. The main damages observed in the tested batteries are related to sludge, corrosion and self-discharge, leading to gradual capacity losses. Results here presented show a different behaviour concerning degradation between both batteries. Following this we present a discussion about the selection of the voltage to which the degradation test should be performed. We propose to use the gassing voltage obtained from the charge curve. Additionally, at the end of the overcharge tests, self-discharge have been determined in both batteries at 25° and 71° C. Keywords: Batteries - 1: Degradation - 2: Lifetime -3
