A123 Grid Battery System Single Rack Evaluation

Southern California Edison (SCE) is performing accelerated life cycle testing on a subsystem of A123’s Grid Battery System (GBS). SCE’s laboratory testing is being performed on one rack containing 6 modules that provided 100 kW and 23 kWh. The full GBS is a 2MW 500kWh system composed of 18 racks with 8 modules in each. A test profile composed of 1C and 2C 100% depth of discharge (DOD) cycles was produced to apply 9 cycles per day. Assuming the full system will be used once per day, four months of testing corresponds to the cycles that would be applied over three years of operation. To help track battery performance throughout the testing, Reference Performance Tests (RPTs) are performed every 300 cycles (which corresponds to just over one month). The rack is contained in an environmentally controlled chamber at 20°C during all cycling to simulate the thermal conditions in the GBS container. Over 3000 test cycles have been completed on the GBS system. Approximately 10% decay in capacity has been observed for all power levels. At 80% DOD the available power has decreased only 3%. After approximately the 1200th cycle, a four month pause in testing occurred. Upon restarting the cycling, a significant decrease in capacity was observed. However, the capacity did not decay as quickly. After about the 2000th cycle, the capacity trend resumed the initial rate of decay. This pause in testing has produced interesting conclusions relating to the relationship of calendar life and accelerated cycling which could have significant impacts on electric vehicle or utility application of lithium-ion batteries. This report focuses entirely on the laboratory testing of the GBS single rack. Future analysis will combine these results with those of other SCE tests to produce conclusions regarding the application of the GBS on SCE’s grid.