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The long tailpipe

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Chevrolet Volts charging at a solar-powered charging station in Toronto. The carbon footprint of plug-in electric vehicles depends on the fuel and technology used for electricity generation.

The long tailpipe is an argument stating that usage of electric vehicles does not always result in fewer emissions (e.g. greenhouse gas emissions) compared to those from non-electric vehicles. While the argument acknowledges that plug-in electric vehicles operating in all-electric mode have no greenhouse gas emissions from the onboard source of power, it claims that these emissions are shifted from the vehicle tailpipe to the location of the electrical generation plants. From the point of view of a well-to-wheel assessment, the extent of the actual carbon footprint depends on the fuel and technology used for electricity generation, as well as the impact of additional electricity demand on the phase-out of fossil fuel power plants.

Description

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See also: Greenhouse gas emissions in plug-in electric vehicles, air pollution and carbon emissions in electric cars, and greenhouse gas emissions in plug-in hybrids

Plug-in electric vehicles (PEVs) operating in all-electric mode do not emit greenhouse gases from the onboard source of power but emissions are shifted to the location of the generation plants. From the point of view of a well-to-wheel assessment, the extent of the actual carbon footprint depends on the fuel and technology used for electricity generation. From the perspective of a full life cycle analysis, the electricity used to recharge the batteries must be generated from renewable or clean sources such as wind, solar, hydroelectric, or nuclear power for PEVs to have almost none or zero well-to-wheel emissions.[1][2] On the other hand, when PEVs are recharged from coal-fired plants, they usually produce slightly more greenhouse gas emissions than internal combustion engine vehicles and higher than hybrid electric vehicles.[1][3]

Because plug-in electric vehicles do not produce emissions at the point of operation are often perceived as being environmentally friendlier than vehicles driven through internal combustion. Assessing the validity of that perception is difficult due to the greenhouse gases generated by the power plants that provide the electricity to charge the vehicles' batteries.[4][5] For example, the New York Times reported that a Nissan Leaf driving in Los Angeles would have the same environmental impact as a gasoline-powered car with 79 mpg‑US (3.0 L/100 km; 95 mpg‑imp) compared to the same trip in Denver would only have the equivalent of 33 mpg‑US (7.1 L/100 km; 40 mpg‑imp).[6] The U.S. Department of Energy published a concise description of the problem: "Electric vehicles (EVs) themselves emit no greenhouse gases (GHGs), but substantial emissions can be produced 'upstream' at the electric power plant."[7]

A recent study[8] by the German IfW shows that the increased electricity demand, and the resulting delay in the shutdown of coal-fired power plants in Germany, causes electric vehicles to have 73% higher CO2 emissions than Diesel vehicles.

Carbon footprint in selected countries

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A study published in the UK in April 2013 assessed the carbon footprint of plug-in electric vehicles in 20 countries. As a baseline the analysis established that manufacturing emissions account for 70 g CO2/km. The study found that in countries with coal-intensive generation, PEVs are no different from conventional petrol-powered vehicles. Among these countries are China, Indonesia, Australia, South Africa and India. A pure electric car in India generates emissions comparable to a 20 mpg‑US (12 L/100 km; 24 mpg‑imp) petrol car. The country ranking was led by Paraguay, where all electricity is produced from hydropower, and Iceland, where electricity production relies on renewable power, mainly hydro and geothermal power. Resulting carbon emissions from an electric car in both countries are 70 g CO2/km, which is equivalent to a 220 mpg‑US (1.1 L/100 km; 260 mpg‑imp) petrol car, and correspond to manufacturing emissions. Next in the ranking are other countries with similar low carbon electricity generation, including Sweden (mostly hydro and nuclear power ), Brazil (mainly hydropower) and France (predominantly nuclear power). Countries ranking in the middle include Japan, Germany, the UK and the United States.[9][10][11]

The following table shows the emission intensity estimated in the study for each of the 20 countries, and the corresponding emissions equivalent in miles per US gallon of a petrol-powered car.

Note that changes since 2013 will make significant changes to the figures, for example the UK emission factor for electricity in 2013 was 0.44546 kg/kWh,[12] by 2023 this had dropped to 0.207074 kg/kWh,[13] about 46% of the 2013 figure, which would move the UK into the "Low carbon" section.

Country comparison of full life cycle assessment
of greenhouse gas emissions resulting from charging plug-in electric cars and
emissions equivalent in terms of miles per US gallon of a petrol-powered car[9][11]
Country PEV well-to-wheels
carbon dioxide equivalent
emissions per electric car
expressed in (CO2e/km)		 Power
source		 PEV well-to-wheels
emissions equivalent
in terms of mpg US
of petrol-powered car		 Equivalent
petrol car
 Paraguay 70 Low carbon 218 mpg‑US (1.08 L/100 km) Hybrid
multiples
 Iceland 70 217 mpg‑US (1.08 L/100 km)
 Sweden 81 159 mpg‑US (1.48 L/100 km)
 Brazil 89 134 mpg‑US (1.76 L/100 km)
 France 93 123 mpg‑US (1.91 L/100 km)
 Canada 115 Fossil light 87 mpg‑US (2.7 L/100 km) Beyond
hybrid
 Spain 146 61 mpg‑US (3.9 L/100 km)
 Russia 155 57 mpg‑US (4.1 L/100 km)
 Italy 170 Broad mix 50 mpg‑US (4.7 L/100 km) New
hybrid
 Japan 175 48 mpg‑US (4.9 L/100 km)
 Germany 179 47 mpg‑US (5.0 L/100 km)
 United Kingdom 189 44 mpg‑US (5.3 L/100 km)
 United States 202 Fossil heavy 40 mpg‑US (5.9 L/100 km) Efficient
petrol
 Mexico 203 40 mpg‑US (5.9 L/100 km)
 Turkey 204 40 mpg‑US (5.9 L/100 km)
 China 258 Coal based 30 mpg‑US (7.8 L/100 km) Average
petrol
 Indonesia 270 28 mpg‑US (8.4 L/100 km)
 Australia 292 26 mpg‑US (9.0 L/100 km)
 South Africa 318 24 mpg‑US (9.8 L/100 km)
 India 370 20 mpg‑US (12 L/100 km)
Note: Electric car manufacturing emissions account for 70 g CO2/km
Source: Shades of Green: Electric Cars’ Carbon Emissions Around the Globe, Shrink That Footprint, February 2013.[11]

Carbon footprint in the United States

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In the case of the United States, the Union of Concerned Scientists (UCS) conducted a study in 2012 to assess average greenhouse gas emissions resulting from charging plug-in car batteries from the perspective of the full life-cycle (well-to-wheel analysis) and according to fuel and technology used to generate electric power by region. The study used the Nissan Leaf all-electric car to establish the analysis baseline, and electric-utility emissions are based on EPA's 2007 estimates. The UCS study expressed the results in terms of miles per gallon instead of the conventional unit of grams of greenhouse gases or carbon dioxide equivalent emissions per year in order to make the results more friendly for consumers. The study found that in areas where electricity is generated from natural gas, nuclear, hydroelectric or renewable sources, the potential of plug-in electric cars to reduce greenhouse emissions is significant. On the other hand, in regions where a high proportion of power is generated from coal, hybrid electric cars produce less CO2 equivalent emissions than plug-in electric cars, and the best fuel efficient gasoline-powered subcompact car produces slightly less emissions than a PEV. In the worst-case scenario, the study estimated that for a region where all energy is generated from coal, a plug-in electric car would emit greenhouse gas emissions equivalent to a gasoline car rated at a combined city/highway driving fuel economy of 30 mpg‑US (7.8 L/100 km; 36 mpg‑imp). In contrast, in a region that is completely reliant on natural gas, the PEV would be equivalent to a gasoline-powered car rated at 50 mpg‑US (4.7 L/100 km; 60 mpg‑imp).[14][15]

The following table shows a representative sample of cities within each of the three categories of emissions intensity used in the UCS study, showing the corresponding miles per gallon equivalent for each city as compared to the greenhouse gas emissions of a gasoline-powered car:

Regional comparison of full life cycle assessment
of greenhouse gas emissions resulting from charging plug-in electric vehicles
expressed in terms of miles per gallon of a gasoline-powered car with equivalent emissions[14][16][17]
Rating scale
by emissions intensity
expressed as
miles per gallon		 City PEV well-to-wheels
carbon dioxide equivalent
(CO2e) emissions per year
expressed as mpg US		 Percent reduction in
CO2e emissions
compared with
27 mpg US average
new compact car		 Combined EPA's rated
fuel economy and
GHG emissions
for reference
gasoline-powered car[18]
Best
Lowest CO2e emissions
equivalent to
over50 mpg‑US (4.7 L/100 km)		 Juneau, Alaska 112 mpg‑US (2.10 L/100 km) 315% 2012 Toyota Prius/Prius c
50 mpg‑US (4.7 L/100 km)
San Francisco 79 mpg‑US (3.0 L/100 km) 193%
New York City 74 mpg‑US (3.2 L/100 km) 174%
Portland, Oregon 73 mpg‑US (3.2 L/100 km) 170% Greenhouse gas emissions (grams/mile)
Boston 67 mpg‑US (3.5 L/100 km) 148% Tailpipe CO2 Upstream GHG
Washington, D.C. 58 mpg‑US (4.1 L/100 km) 115% 178 g/mi (111 g/km) 44 g/mi (27 g/km)
Better
Moderate CO2e emissions
equivalent to between
41 mpg‑US (5.7 L/100 km) to
50 mpg‑US (4.7 L/100 km)		 Phoenix, Arizona 48 mpg‑US (4.9 L/100 km) 78% 2012 Honda Civic Hybrid
44 mpg‑US (5.3 L/100 km)
Miami 47 mpg‑US (5.0 L/100 km) 74%
Houston 46 mpg‑US (5.1 L/100 km) 70% Greenhouse gas emissions (grams/mile)
Columbus, Ohio 41 mpg‑US (5.7 L/100 km) 52% Tailpipe CO2 Upstream GHG
Atlanta 41 mpg‑US (5.7 L/100 km) 52% 202 g/mi (125 g/km) 50 g/mi (31 g/km)
Good
Highest CO2e emissions
equivalent to between
31 mpg‑US (7.6 L/100 km) to
40 mpg‑US (5.9 L/100 km)		 Detroit 38 mpg‑US (6.2 L/100 km) 41% 2012 Chevrolet Cruze
30 mpg‑US (7.8 L/100 km)
Des Moines, Iowa 37 mpg‑US (6.4 L/100 km) 37%
St. Louis, Missouri 36 mpg‑US (6.5 L/100 km) 33% Greenhouse gas emissions (grams/mile)
Wichita, Kansas 35 mpg‑US (6.7 L/100 km) 30% Tailpipe CO2 Upstream GHG
Denver 33 mpg‑US (7.1 L/100 km) 22% 296 g/mi (184 g/km) 73 g/mi (45 g/km)
Source: Union of Concerned Scientists, 2012.[14]
Notes: The Nissan Leaf is the baseline car for the assessment, with an energy consumption rated by EPA at 34 kWh/100 mi or 99 miles per gallon gasoline equivalent (2.4 L/100 km) combined.
The ratings are based on a region's mix of electricity sources and its average emissions intensity over the course of a year. In practice the electricity grid is very dynamic, with the mix of
power plants constantly changing in response to hourly, daily and seasonal electricity demand, and availability of electricity resources.

An analysis of EPA power plant data from 2016 showed improvement in mpg-equivalent ratings of electric cars for nearly all regions, with a national weighted average of 80 mpg for electric vehicles.[19] The regions with the highest ratings include upstate New York, New England, and California at over 100 mpg, while only Oahu, Wisconsin, and part of Illinois and Missouri are below 40 mpg, though still higher than nearly all gasoline cars.

Criticism

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The long tailpipe has been the target of criticism, ranging from claims that many estimates are methodologically flawed to estimates that state that electricity generation in the United States will become less carbon-intensive over time.[20] Tesla Motors CEO Elon Musk published his own criticism of the long tailpipe.[21] The extraction and refining of carbon based fuels and its distribution is in itself an energy intensive industry contributing to CO2 emissions. In 2007 U.S. refineries consumed 39353 million kWh, 70769 million lbs of steam and 697593 million cubic feet of Natural Gas. And the refining energy efficiency for gasoline is estimated to be, at best, 87.7%.[22]

References

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  1. ^ a b Sperling, Daniel and Deborah Gordon (2009). Two billion cars: driving toward sustainability. Oxford University Press, New York. pp. 22–26 and 114–139. ISBN 978-0-19-537664-7.
  2. ^ David B. Sandalow, ed. (2009). Plug-In Electric Vehicles: What Role for Washington? (1st. ed.). The Brookings Institution. pp. 2–5. ISBN 978-0-8157-0305-1. See definition on pp. 2.
  3. ^ "The Dirty Truth about Plug-in Hybrids, Made Interactive". Scientific American. July 2010. Retrieved 2010-10-16. Click on the map to see the results for each region.
  4. ^ "Analyzing effects from well to wheel to air (the long tailpipe)". Green Transportation. 27 Oct 2011. Retrieved 20 December 2012.
  5. ^ Hickman, Leo (5 October 2012). "Are electric cars bad for the environment?". The Guardian. Retrieved 20 December 2012.
  6. ^ STENQUIST, PAUL (30 April 2012). "How Green Are Electric Cars? Depends on Where You Plug In". New York Times. Retrieved 20 December 2012.
  7. ^ "Electric Power". Energy Information Administration. U.S. Department of Energy. Retrieved 21 December 2012.
  8. ^ "Electric Mobility and Climate Protection: A Substantial Miscalculation". Institut fuer Wirtschaftsforschung. Retrieved 7 July 2020.
  9. ^ a b "India named least green country for electric cars". The Guardian. 2013-02-07. Retrieved 2013-07-08.
  10. ^ Michaël Torregrossa (2013-03-21). "Véhicules électriques et émissions de CO2 – de 70 à 370 g CO2/km selon les pays" [Electric Vehicles and CO2 emissions - 70 to 370 g CO2/km by country] (in French). Association pour l'Avenir du Véhicule Electrique Méditerranéen (AVEM). Retrieved 2013-07-08.
  11. ^ a b c Lindsay Wilson (February 2013). "Shades of Green: Electric Cars' Carbon Emissions Around the Globe". Shrink That Footprint. Retrieved 2013-07-08.
  12. ^ "Greenhouse gas reporting - Conversion factors 2013".
  13. ^ "Greenhouse gas reporting: Conversion factors 2023". 28 June 2023.
  14. ^ a b c Don Anair and Amine Mahmassani (April 2012). "State of Charge: Electric Vehicles' Global Warming Emissions and Fuel-Cost Savings across the United States" (PDF). Union of Concerned Scientists. Retrieved 2012-04-16. pp. 16-20.
  15. ^ Paul Stenquist (2012-04-13). "How Green Are Electric Cars? Depends on Where You Plug In". The New York Times. Retrieved 2012-04-14.
  16. ^ Paul Stenquist (2012-04-13). "Carbon In, Carbon Out: Sorting Out the Power Grid". The New York Times. Retrieved 2012-04-14. See map for regional results
  17. ^ Paul Stenquist (2012-04-13). "When it Comes to Carbon Dioxide, Lower is Better and Zero is Perfect". The New York Times. Retrieved 2012-04-14.
  18. ^ "Compare side-by-side". U.S. Department of Energy and U.S. Environmental Protection Agency. 2012-04-13. Retrieved 2012-04-15. Energy and Environment tab: cars selected Toyota Prius, Prius c, Honda Civic Hybrid, and Chevrolet Cruze automatical, all model year 2012.
  19. ^ "New Data Show Electric Vehicles Continue to Get Cleaner". Union of Concerned Scientists. 2018-03-08. Retrieved 2018-08-26.
  20. ^ Hall, Dean (5 Apr 2010). "Holes in the Long Tailpipe". neoHOUSTON. Retrieved 21 December 2012.
  21. ^ Musk, Elon. "The Secret Tesla Motors Master Plan (just between you and me)". Tesla Blog. Tesla Motors. Retrieved 20 December 2012.
  22. ^ Wang, Michael (Mar 2008). "Estimation of Energy Efficiencies of U.S. Petroleum Refineries". Argonne National Laboratory. Retrieved 6 March 2016.
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