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 paper 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 and 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 10 methods at nine charging station locations around the United States. Across the methods, we found an 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 in order to achieve results that are more consistent across studies and allow for soundly supported policy decisions. The paper addresses this issue by offering a set of recommendations for determining an appropriate model type on the basis of the load characteristics and study objectives.

Marginal Life-Cycle Greenhouse Gas Emissions of Electricity Generation in Portugal and Implications for Electric Vehicles

“…The marginal emission factors used in this analysis were calculated based on regression models that use historical data. As noted by [13], whilst these models describe the electricity system historically, they do not capture potential changes in the system over time, and thus can only be used to assess changes in electricity demand in the near term [16]. Nevertheless, only small changes to the electricity system portfolio are expected to occur in the next few years, and as new data becomes available, it is possible to regularly update the analysis to reflect the changes in the electricity sector.…”

“…Additionally, electricity trading with neighboring systems (Spain) was not accounted for because the percent of electricity imported is low. In order to determine the effects of electricity trading, power system optimization models should be used [16].…”

“…On the other hand, a smaller group of studies looked at EVs as a new load added to the electricity system and assessed how the system would respond to this change by determining the marginal electricity supply and corresponding emissions (e.g., [12][13][14][15]). The different approaches used to determine electricity emissions often lead to very distinct results, which is problematic because of the importance of electricity emissions to the overall EV impacts [16].…”

Effects on Greenhouse Gas Emissions of Introducing Electric Vehicles into an Electricity System with Large Storage Capacity

“…When the transient behavior of generation and demand must be modeled, further complexities and uncertainties arise (Ryan et al. ).…”

“…Pumped storage makes the timing of variations in demand immaterial. This removes the problems identified by Ryan and colleagues () in calculating grid emissions with transient generation and loads: overall changes can be assessed by simple energy balances on long‐term average demand and supply without having to examine short‐term operations. In this article, developments in both the energy system and the vehicle fleet are modeled on an annual basis with changes considered over a period of 10 years.…”