Model of Cost and Mass for Compact Sized Lightweight Automobiles using Aluminum & High Strength Steel
In this paper, we consider interactions between life cycle emissions and materials flows associated with lightweighting automobiles. The study begins by developing scenarios for lightweighting a specific compact sized vehicle based on a Ford Focus. Both aluminum and high strength steel are used, and specific levels of lightweighting are considered between 6% and 23% based on literature references and discussions with industry experts. Using automotive simulations and literature estimations for cost, we estimate improvements in fuel economy and increases in cost relative to the baseline vehicle. By incorporating emissions factors associated with producing aluminum and high strength steel, over a range of possible values dependent for instance on region of the world where these materials are produced, we compare the increased emissions associated with producing the vehicle with the saved emissions during use following from lightweighting. This yields a calculation of how many years it takes to recover the extra greenhouse gas GHG emissions required in production to create the lightweight vehicle. We observe a 2-12 year GHG payback for the 6% lightweighting scenario, a 2-7 year GHG payback for the 11% lightweighting scenario, and a 4-9 year GHG payback for the 23% lightweighting scenario. We also observe that the cost to remove GHG emissions per kilogram by lightweighting is lowest for the 23% case. In principle, these payback times can be shortened for aluminum intensive vehicles by closed-loop recycling of wrought aluminum (i.e., using secondary wrought aluminum), which is not practiced today. However, over a 15-year time horizon this is unlikely to make much difference due to a lack of secondary wrought aluminum and the expected growth in the demand for vehicles. Cost analyses demonstrate that lightweight vehicles have favorable economics for consumers.