Energy storage systems play an important role in increasing the reliability, efficiency, and cleanliness of the grid. Therefore, there are basically two ways to provide grid services:

1.  Vehicle-to-grid (V2G) application utilizes the battery for grid services, whereas the battery is still in the vehicle.
2. Use a battery system to store the energy

However, the cost of batteries represents a prominent barrier to their use as grid-connected energy storage. To solve this issue, the cost of batteries can be decreased by lowering material costs, enhancing process efficiencies and increasing production volume. Another solution is to reuse the batteries from the electric vehicles.  In addition, initial investigations into the further use of electric vehicle batteries in other applications were motivated by the need to decrease the capital cost of electric vehicles.

Actually, the used EVs (PHEV, HEV and BEV) batteries are still expected to be capable of storing and delivering substantial energy, it is possible that they satisfy the requirements of stationary applications. In stationary applications, the weight and volume of the battery systems are not a sever constraints like in the automotive applications. In addition to that a fraction of the batteries cost can be covered after they have been retired from vehicular service by reusing them in other applications. Thus, the total lifetime value of the battery will increase when the remaining capacity of batteries is invested to meet the requirements of the other applications.

The main target of this article is to investigate the possibility of reusing Lithium-ion batteries, which have been retired from vehicular service, in the stationary applications. To achieve the goals of this study, several unresolved issues and potential barriers have been identified, sorted and solved during the development of the reuse process, including:

• Non-standardized battery modules, which are used in different patterns of the vehicle, will cause a difficulty in finding battery modules with similar capacity for building a second-life battery pack;
• Battery model of the second-life batteries;
• The quick characterization test to evaluate the state-of-health (SoH), which plays an important role in order to save time, cost and effort for evaluating, sorting and assembling the second-life battery;
• Effective factors to increase the life cycle of the used batteries;
• Effective battery management system (BMS) should be developed not only to be used for balancing the voltage and SoC of cells/blocks, but also to decrease power loss and power consumption in BMS itself and to increase the overall efficiency of the second life battery pack;
• Energy management system should be developed to discharge and charge the used battery modules based on their performances; and,
• Power electronic converter should be selected carefully in order to increase the life cycles of the second-life modules with high efficiency.

This paper illustrates a market size of second-life battery storage systems in stationary applications. Afterwards, it shows a comprehensive technical analysis by addressing all aspects of a battery’s life cycle in order to get the best second-use strategies, followed by a comprehensive test program to verify the findings, particularly the life of batteries. Based on these tests, some goals have been achieved as follows:

• Developing a second life battery model so that the performance of these batteries can be monitored through the estimation and evaluation of different battery parameters.
• Developing a proper state of health (SoH) estimation technique to evaluate the performance of the batteries and thus quickly sort the used batteries.

After testing and sorting the used batteries, this research also presents the method to refurbish the used modules by using battery management system. Indeed, these cells have been monitored by using a proper battery management system, which has been designed to balance different types of batteries and to decrease the energy loss in the BMS itself. Afterwards, the second-life modules with BMS have been connected to the grid through a specific power electronic converter. Besides, the energy management system has been designed to ensure that the load current is shared between the second-life modules in order to increase the life cycles of these modules. The simulation and practical results related to this research are presented and discussed.

Acknowledgement

We acknowledge Flanders Make for supporting our team. We also acknowledge Vito for supporting this Project.