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

Rita Garcia,Fausto Freire

doi:10.3390/resources5040041

Abstract

This article assesses marginal greenhouse gas (GHG) emissions of electricity generation in Portugal to understand the impact of activities that affect electricity demand in the near term. In particular, it investigates the introduction of electric vehicles (EVs) in the Portuguese light-duty fleet considering different displacement and charging scenarios (vehicle technologies displaced, EV charging time). Coal and natural gas were identified as the marginal sources, but their contribution to the margin depended on the hour of the day, time of year, and system load, causing marginal emissions from electricity to vary significantly. Results show that for an electricity system with a high share of non-dispatchable renewable power, such as the Portuguese system, marginal emissions are considerably higher than average emissions. Because of the temporal variability in the marginal electricity supply, the time of charging may have a major influence on the GHG emissions of EVs. Off-peak charging leads to higher GHG emissions than peak charging, due to a higher contribution of coal to the margin. Furthermore, compared to an all-conventional fleet, EV introduction causes an increase in overall GHG emissions in most cases. However, EV effects are very dependent on the time of charging and the assumptions about the displaced technology.

Highlights

Measures which aim to reduce energy consumption and greenhouse gas (GHG) emissions by promoting the increase in energy efficiency of end-use applications, the temporal shifting of electricity use, or the use of electricity over other fuels have an impact in the grid load profile
That is the case with the introduction of electric vehicles (EVs) in a fleet, which increases electricity demand by shifting the energy source used for transportation from mainly petroleum-based fuels to electricity
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])

Summary

Introduction

Measures which aim to reduce energy consumption and greenhouse gas (GHG) emissions by promoting the increase in energy efficiency of end-use applications, the temporal shifting of electricity use, or the use of electricity over other fuels have an impact in the grid load profile. Most life-cycle assessment (LCA) studies on EVs assumed that EVs are part of the total load of the system and used average emission factors for electricity supply to assess EV environmental impacts (e.g., [1,2,3,4,5,6,7,8]). These studies have found that vehicle use dominates over the vehicle production phase regarding energy consumption and GHG emissions, for fossil-based electricity mixes [8]. The model allows for the assessment of: (i) electricity demand by the EV fleet in each year (see Table S1); and (ii) changes in emissions from personal road vehicles

Objectives

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Results

Conclusion