We are pleased to take this opportunity to respond to Christoff Koffler, Jinlong Marshall Wang, and Kurt Buxmann's comments regarding our article “Using Nested Average Electricity Allocation Protocols to Characterize Electrical Grids in Life Cycle Assessment: A Case Study of U.S. Primary Aluminum Production” (Colett et al. 2016). Koffler and colleagues (2016) indicate that our article “provides good insights into the challenges associated with quantifying GHG emissions from electricity consumption,” which was our aim. Our objective in the article was to create and apply an allocation method that enables life cycle assessment (LCA) practitioners to estimate emission factors for electricity consumption using public data while balancing accuracy and modeling complexity.
This research was conducted as part of a U.S. Department of Energy Clean Energy Research Center Clean Vehicle Consortium project to study greenhouse gas (GHG) emission impacts of vehicle electrification and lightweighting strategies, including material sourcing decisions. We focused on the U.S. primary aluminum industry as a case study because of its electricity dependence, enabling us to study the sensitivity of emission factors to the allocation method used. We make no claim that our case-study GHG estimates should be used as standards, but present them in comparison to previous estimates produced by other methods to highlight the importance of the choice of allocation method on results.