Comparative Assessment of Models and Methods to Calculate Grid Electricity Emissions

Abstract

Due to the complexity of power systems, tracking emissions attributable to a specific electrical load is a daunting challenge, but essential for many environmental impact studies. Currently, no consensus exists on appropriate methods for quantifying emissions from particular electricity loads. This thesis reviews a wide range of the existing methods, detailing their functionality, tractability, and appropriate use. We identified and reviewed 32 methods and models and classified them into two distinct categories: empirical data & relationship models and power system optimization models. To illustrate the impact of method selection, we calculate the CO2 combustion emissions factors associated with electric vehicle charging using ten methods at nine charging station locations around the U.S. Across the methods, we found up to 68% difference from the mean CO2 emissions factor for a given charging site among both marginal and average emissions factors and up to a 63% difference from the average across average emissions factors. Our results underscore the importance of method selection and the need for a consensus on approaches appropriate for particular loads and research questions being addressed to achieve results that are more consistent across studies and allow for soundly supported policy decisions. The thesis addresses this issue by offering a set of recommendations for determining an appropriate model type based the load characteristics and study objectives.