Optimization of battery pack assembly of second life cells to reduce costs

Abstract: Batteries account for 50% of the overall cost of solar home systems (SHS). The battery packs degrade over time and when they reach 70% state of health (SOH), the whole SHS is discarded. In the predominantly rural off-grid context, battery replacements are expensive and impractical. The customers are often dozens of km away from any sales point. Furthermore, recycling schemes are often limited in the developing world, meaning that old batteries are sometimes discarded in unsafe ways. As the market grows, the environmental impact of this will only get larger. Solaris Offgrid, a premier name in the Solar Offgrid industry, is innovating two solutions designed to tackle this issue; a smart multi-battery packmanager and an easy to recycle battery pack design with cell by cell management. The current study is based on a lossless cell balancing design, where in the charge and discharge cycles of each cell in the string are monitored and to efficiently avoid overcharge and over-discharge. Implementing this strategy reduces the degradation of these batteries which extends the battery life of SHS. A sensitivity analysis is performed to analyze the environmental benefit gained by implementing lossless cell balancing. The thesis provides a literature study on the different battery terminologies, types of batteries used in SHS and, various cell-balancing techniques used today. This is followed by the design of a lossless cell balancing technique with minimal losses.