LEAD-ACID BATTERY RESPONSE TO VARIOUS FORMATION LEVELS AND METHODS: DETERMINING THE OPTIMAL FORMATION LEVEL FOR OFF-GRID SOLAR APPLICATIONS

Abstract

A significant number of people in the world are without electricity service, the majority of which are located in rural areas where extending the electricity grid is not economically feasible. Off-grid solar photovoltaic technology has been identified as the most prominent option to electrify these rural areas, of which lead-acid storage batteries are a major component.

The manufacture of lead-acid batteries requires an electrochemical activation process called “formation”. Formation is poorly defined in the public literature as it is considered confidential by battery manufacturers, and because solar storage batteries are only now a significant market. Thus, the objective of this thesis project is to determine the optimal formation level and method for the manufacturing of lead-acid batteries intended for the off-grid solar storage market. In order to determine the optimal formation level, ELG15 lead-acid battery cells with a rated capacity of 231 Ah and positive plate thicknesses of 4.32 mm were formed using two different formation algorithms in a laboratory setting to formation levels ranging from 0.70 to 7.04 times the theoretical capacity of the cell. Following the completion of 10 deep-cycles per cell, the ideal formation level for this cell was determined to be between 2.75 and 3.55 times its theoretical capacity. This newly recommended formation range for off-grid solar applications was found to be complementary to the range recommended in literature for conventional applications of 1.30 to 2.50 times the theoretical capacity of the cell.

In order to determine the optimal formation method, ELG15 cells were formed using the floor container, submerged container, circulated electrolyte, and tank formation methods used interchangeably at Surrette Battery Company, and to three formation levels equivalent to 80 %, 100 %, and 120 % of the standard formation algorithm for each respective formation method. Subsequently, three cells per formation level (i.e., a module) were deep-cycled simultaneously using a series configuration. By comparing the initial discharge capacity results of the 12 different modules as a function of theoretical capacity, the modules obtained using the circulated electrolyte formation method outperformed all other formation methods, and showed no disadvantages with respect to total formation time when compared to the other formation methods. The optimal formation method was determined to be the circulated electrolyte formation method, at a level equivalent to 2.89 times the theoretical capacity of the cell.