From Ferry to Home

Abstract

The growing number of retired mobility batteries creates both a waste-management challenge and an opportunity to extend the useful life of resource-intensive battery systems. Although these batteries may no longer satisfy the demanding energy or power requirements for mobility, they may still have sufficient capacity for less demanding stationary storage applications. While most previous studies focus on passenger electric vehicle batteries, this thesis investigates to what extent retired heavy-duty NMC batteries from an electric ferry can provide environmentally beneficial second-life storage in a photovoltaic-coupled residential energy system compared with newly produced LFP batteries.
An integrated assessment framework combines one physics based and two empirical battery degradation models with an operational ferry load profile, weather and irradiance data, and the PVMD Toolbox. The framework follows a 604.8 kWh NMC battery from first-life ferry operation into second-life stationary storage. Three stationary storage sizes of 403.2 kWh, 705.6 kWh and 1008 kWh assembled from second-life ferry batteries were evaluated in the same PV-residential system. Their environmental performance was assessed through a prospective life cycle assessment using system expansion. The largest reduction in total impacts compared to using new batteries, approximately 12%, is achieved by the 705.6 kWh second-life system, which also has the lowest impact per kilowatt-hour of battery energy delivered.
However, a properly sized new battery system has 25% lower impacts per delivered function than an undersized second-life system, demonstrating that sizing can be as important as choosing a repurposed battery. Furthermore, the scenario results indicate that the environmental performance depends strongly on the grid-electricity mix. When the 2030 electricity mix, which still contains approximately 25% fossil energy, is used, the total normalized and weighted impacts of the no-battery case are approximately 33% higher than when the cleaner prospective 2050--2070 electricity mix is applied. The results demonstrate that retired ferry batteries can provide environmentally beneficial second-life storage, but that this benefit is not automatic. It depends not only on the battery condition, but on the combined effects of system sizing, lifetime, delivered energy, efficiency and the used electricity mix.