Design of Energy Storage System using Retired Valve Regulated Lead Acid (VRLA) Batteries in Substations

Valve regulated lead acid (VRLA) batteries widely used in substations still have large residual capacities when they are retired, so they can be reused in battery energy storage systems (BESS). A reusing BESS for retired VRLA batteries is designed in this paper, and its main function is peak-load shifting. The scale of this reusing BESS is 187 kW/1.87 MWh, and 3120 retired VRLA batteries are used. The reusing BESS can be divided into five sub-BESSes. Each sub-BESS is arranged in a container and consists of six parallel battery packs. Each battery pack consists of 104 battery cells in series, and it is connected to the main grid through a power conversion system (PCS). Meanwhile, each battery pack is managed by a battery management system (BMS). The BMS can achieve the functions such as battery dynamic equalization, overvoltage/undervoltage protection of each battery cell, and automatic isolation of defective batteries. Finally, the advantages and disadvantages of this reusing BESS are demonstrated by comparing it with another design of the reusing BESS, and the economic performance of this reusing BESS is evaluated.