M. Starke, D. Spiers, B. Taube
Keywords: repurposing used EV batteries, secondary use systems, technoeconomic analysis and benchmarking, electric vehicles, system integration
Summary:Energy storage technologies are expected to revolutionize the electric power grid by reducing energy costs, providing means to integrate renewables, and increasing grid reliability and resiliency. Numerous demonstration projects of energy storage technologies funded by the Department of Energy have already demonstrated the ability for grid scale energy storage systems to perform these functions. However, capital investment costs have largely limited the wide scale deployment of these technologies to niche cost effective applications. Today, the wide adoption of electric vehicles could potentially change this truth. In the last two decades, the electric vehicle market has seen a spur of innovation and growth that has led to a revolution of battery systems, largely of the lithium-ion variety. Still, these battery systems have an expected life and finding a role for these systems following the electric vehicle application is critical. There are three R’s have been derived to support this research: remanufacture, repurpose, and recycle. Recycling is difficult to market, as the cost to extract the valuable materials is usually not sufficient to perform the work. Remanufacturing the systems into new electric vehicle battery systems only applies to lightly aged systems where capacity is still near the original. For the rest of the electric vehicle systems, repurposing the battery systems for new applications appears to be an opportunity. This concept has been provided the title of secondary use energy storage technology. The application of a secondary use battery systems is not straightforward and does not come for free. One, the system must be integrated with power electronic conversion stages to convert the direct current from the battery system to the required 60Hz output for the grid. Furthermore, any supporting power conditioning and isolation systems could potentially be required. Two, they system must be containerized into a National Electrical Manufacturers Association type enclosure, as many grid energy storage systems are expected to be exposed to the environment. This includes considerations for environment conditioning within this system. Three, the system needs integration with many different protection layers (both software and hardware) to isolate sub-component failures. This can require either integration with electric vehicle manufacturer battery management system or integration of a new system which requires repacking. All of these different considerations lead to a wide variety of energy storage systems with varying levels of quality and expected life. In this paper, an examination of the varying scales of secondary use systems will be discussed and referenced in terms of potential life versus cost. In the lowest form of repacking, a battery system is simply extracted from an electric vehicle, left within the automotive enclosure and included into a container. At the higher stages, the battery system is opened and the modules are graded and separated into similar units for reintegration with a new battery management system. The life expectancy and grid integration requirements between these different offerings can be extreme.