Ask an Expert: Electric Vehicle Emissions
Do electric vehicles really have zero emissions?
An EV produces at least 30% fewer source emissions than an internal combustion engine (ICE) vehicle. Vehicles using gasoline engines emit carbon dioxide, carbon monoxide, unburned hydrocarbons, particulate matter, and water. The site emissions from a battery electric vehicle are virtually nonexistent. Electricity produces no fumes or combustion exhaust during vehicle consumption.
A fairer comparison with ICE vehicles would include source emissions. Sources of electricity include coal-fired plants, natural gas turbines, nuclear power plants, and renewable energy sources, such as wind and solar. Source emissions from nuclear and renewable power is virtually zero. Coal-fueled power plants emit roughly 2,249 pounds of CO2 per megawatt-hour (MWh or 1,000 kilowatt-hours, kWh) of electricity produced, according to the latest statistics and analysis from the U.S. Energy Information Administration.
Gasoline vs electric: comparing emissions
Calculate the mass of CO2 emissions per mile of vehicle travel for both types of vehicles. First, let's assume an average ICE vehicle travels 26 miles for each gallon (mpg) of gasoline consumed based on information from the Alternative Fuels Data Center and the Environmental Protection Agency. The combustion of one gallon of gasoline emits about 19.4 pounds of CO2, according to the Department of Energy.
Well-to-vehicle studies from 2003 and 2005 found the energy conversion efficiency of crude oil to gasoline = 0.82
Gasoline-fueled ICE emissions = 19.4 lbs/gal ÷ 26 mpg ÷ 0.82 = 0.91 lbs/mile
For an EV, we'll assume it will travel 5 miles per kWh of battery electric energy consumed. The production of electricity at a coal-fired power plant produces 2,249 pounds of CO2 per MWh of electric energy produced. However, there are losses in transmission and distribution (T&D), battery charging/discharging and electric motor operation.
Power plant-to-EV output shaft electrical efficiency = 0.93 (T&D) x 0.85 (battery) x 0.9 (motor efficiency) = 71 percent
EV emissions = 2,249 lbs/MWh x 1 MWh/1,000 kWh ÷ 5 mi/kWh ÷ 0.71 = 0.63 lbs/mile
So, an EV produces at worst about 30 percent fewer (0.63 vs. 0.91 lbs/mile) source emissions than an ICE vehicle. This finding aligns with what the Department of Energy has learned about electric vehicle efficiency. If the vehicle battery is charged from renewable or nuclear sources, an EV is truly a zero-emissions vehicle.
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