ORALS

As a low cost and mature clean energy source, solar PV generation currently has a high penetration rate especially in sunshine-rich states like California. Battery energy storage systems (BESSs) are frequently incorporated with PV systems as a standard approach to buffer the volatile nature of the PV output. Household small PV and storage systems are popular products in the market. For commercial buildings, similar technology is also available, but normally featuring large centralized battery stacks and consequently high cost. Electric vehicles (EVs) started to enjoy a booming market share since the last decade. The number of EVs on roads is enormous and keeps growing rapidly, and so is the quantity of EV batteries. It is estimated that the first huge wave of EV battery retirement in California will hit in 2025, and retired batteries will keep coming thereafter. EV batteries today, almost exclusively lithium-ion based, cost heavily in both production and recycling. Economically dealing with retired EV batteries is an important topic. Retired EV batteries, though no longer roadworthy, still have considerable capacity for stationary applications where the requirement for energy and power density is not as stringent. As an abundant byproduct from the road, these second-life EV batteries cost much less than new products. Meanwhile, the high cost of (new) batteries in storage systems could be a major discouragement for potential clients, especially small/medium owners. Thus, developing proper technologies to bridge the supply and demand has great significance. The aim of this research is to validate that using second-life EV batteries in BESS for PV and storage system for small/medium sized commercial buildings will reduce the overall cost over serviceable life compared to using new batteries. To achieve this, we are conducting thorough multi-scale analysis and modeling of the second-life EV battery aging process and building degradation models, accordingly developing optimized energy management strategy considering PV and load profiles, and building customized electrical and control systems for site pilot testing. Downscaled lab test bench for electrical and control system and battery cycling lab test system are established in San Diego State University (SDSU), and tests are being conducted. Two pilot testing sites, both with existing solar PV systems but different penetration rate, have been selected and the respective BESSs designing processes are ongoing. Through pilot testing, we aim to achieve overall cost reduction and no less than 35% reduction in initial installation cost, and also to establish the supply chain for similar projects in the future.