UC Davis Institute of Transportation Studies

This paper explores the implications of vehicle recharging on the current electricity grid in California and compares well-to-wheel vehicle emissions for various vehicle and fuel platforms at different times of day and during different seasons. An hourly electricity dispatch model that accounts for supply, demand, and energy transfers among three regions in the state is used to determine the last generator operating in any given hour for a simulated grid and demand curve in 2010. Emissions rates from these generators are attributed to vehicle demand. Plug-in hybrid vehicles are found to reduce emissions compared to conventional hybrids if recharged anytime except during the 2% of hours with the highest marginal electricity emissions rates. This threshold is roughly equal to the emissions rate from an average natural gas combustion turbine (peaking plant) plant operating in California. Battery-electric and fuel cell vehicles using hydrogen from natural gas reformation reduce emissions further. The paper also compares likely near-term marginal greenhouse gas emissions rates from the electricity sector to assumed values in California’s Low Carbon Fuel Standard, and finds that the Statute significantly underestimates likely near-term marginal emissions from the sector, and resulting emissions from plug-in vehicles.