Top 4 Ageing Effects in Lead-Acid Batteries
Lead acid-batteries used in solar PV systems usually last for 8-15 years (500 – 800 full cycles). That is shorter than the 25-40 year lifespan of solar modules. This short life span is caused by the following reversible and irreversible processes, which affect and even amplify each other:
Acid stratification (reversible): It is caused by the “heavy” acid falling to the bottom of the inner battery compartment, causing greater acid density to prevail at the bottom of the cell. This causes a potential difference between the top and bottom parts of the cells, leading to discharge of stored charge. It can be rectified by a gassing charge at every service/maintenance interval, which re-mixes the acid.
Sulphation (irreversible): If the battery is insufficiently recharged after a discharge, it leads to the growth of sulphate crystals that deposit on the plates. They cannot be reconverted to lead or lead oxide, resulting in a decrease in active chargeable mass. Over the life of the battery, this decreases its discharge capacity.
Sludging (irreversible): The changing of volume during charging and discharging causes a loosening of the active material. If there is gas formation within the battery, when flushed out, it collects at the bottom of the battery as lead sludge. If the sludge space on the bottom is too small, short circuits can occur.
Drying out (irreversible): If gassing occurs during charging, the lost water must be replaced. If the battery is not topped up with distilled water in time, it eventually dries out and stops functioning.
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