Improving photovoltaic system sizing by using electrolyte circulation in the lead-acid batteries

Lead-acid batteries are, between all types of batteries, the most used today as storage systems for photovoltaic applications. The sizing of the lead-acid batteries is based on some external parameters, solar irradiation and load consumption, and some battery characteristics, charge capacity and efficiency, depth of discharge, operating voltage, and ageing effects. The improvement of any of these parameters will result in an improvement of the sizing of the lead-acid battery and, consequently, of the sizing of the photovoltaic array. We have studied in this paper the influence of the improved capacity of lead-acid batteries with electrolyte circulation onto the sizing of the lead-acid battery and the PV array. The experimental results have shown that the lead-acid battery capacity can be improved as much as 20% if electrolyte circulation is used. The improvement results in a reduction of up to 30% in the size of the battery if combined with the improvement in the reduction of the battery capacity due to annual cycling and ageing, another beneficial effect of the electrolyte circulation. The reduction of size is extended to the PV array which is affected not only by the above mentioned effects, but also by the higher charge efficiency of the electrolyte circulation battery. The reduction in sizing the PV array can be as much as 41% for the most exigent operating conditions, deep depth of discharge and high discharge rate. The use of an electrolyte circulation system is especially useful in lead-acid batteries for PV systems which must operate at very deep cycling and require a minimum size of the battery block.