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Is Electric Better for the Environment?
The short answer is yes. But the long answer is it depends on what
assumptions one uses. If you compare a Nissan Leaf to a Toyota Prius;
charge the Leaf on coal generated power, and assume there are no emissions in
the extraction and refining of oil, the Prius will edge the Leaf out. But
if you compare a Leaf against a Chevy Malibu, assume one has to at least refine
gasoline, an use a reasonable generation mix, then the Leaf shows a considerable
50% reduction in CO2.
As a licensed professional Engineer I assisted with a grant with our city to
obtain several Nissan Leafs as the city wants to cut vehicle costs and reduce
CO2. Below are the numbers I used to calculate the reduction in CO2.
Here in NE Tennessee we get our power from American Electric Power.
They are mostly coal based, generating 73% of their power from coal, about
double the current
USA average. I used data from AEP's 2015 sustainability report which
lists the amount of KWH sold and the CO2 generated.
The EPA measures wall to wheel efficiency so they include charging
losses in their watts/mile numbers. And because the electricity is
delivered to your house in a form one can use, at a minimum one should adds the
CO2 generated in refining gasoline as a car cannot burn raw oil. At
some point I may add the emissions to get the gasoline from the refinery to the
gas station but if I do so that only improves the case for electric vehicles.
Supporting Data for Green House Gas Emissions
Chevy Malibu - Base case
26 Miles/Gal http://www.fueleconomy.gov/feg/noframes/28629.shtml
0.75 lbs-CO2/mile using 19.6 lbs-CO2/gal
0.89 lbs-CO2/mile Including refining detailed below
Nissan Leaf
340 W/mile - Leaf http://www.fueleconomy.gov/feg/noframes/32154.shtml
0.44 lbs-CO2/mile
0.35 2020 estimated CO2 based on a 3% reduction/year
41% Reduction
50% Reduction with refining included
CO2 emissions for local power 73% Coal
AEP Sustainability Report https://www.aepsustainability.com/fastfacts/docs/2015_GRI-AEP.pdf
122,700,000 Tons/CO2 Reported in 2014
270,430,800,000 lbs-CO2 Conversion (2204lbs/metric ton)
207,211,000,000 KWh Reported in 2014
1.31 lbs-CO2/KWh AEP 2014 Average
593 gms-CO2/kWh
CO2 per gallon of gasoline burned http://www.epa.gov/otaq/climate/documents/420f11041.pdf
8887 g CO2/Gal gasoline
19.575 lbs-CO2/gal converted to lbs. with 454g/lb.
Gasoline Refining
Energy Information Agency report on CO2 emissions in U.S. Manufacturing
http://www.eia.gov/oiaf/1605/ggrpt/pdf/industry_mecs.pdf
Quantity of gasoline produced - EIA - Petroleum & Other LiquidsManufacturing Refining
http://205.254.135.7/dnav/pet/pet_pnp_unc_dcu_nus_a.htm
Petroleum Refineries
Pg. 6 277,600,000 Metric Tons CO2/year
611,830,400,000 lbs. CO2/yr. Conversion (2204 lbs./MT)
2006 15,600,000 US Refining capacity in barrels/day from website above
30 gal/barrel http://www.californiagasprices.com/crude_products.aspx
170,820,000,000 Gal/year Convert to gal/year (*30*365)
3.58 lbs. CO2/gal Additional CO2 generated in refining. Below is another angle from the Department of energy. They estimate that 6 KWh of energy is used in refining. With 6 KWh one can drive my EV about 24 miles, which is farther than the average car goes burning that gasoline.
The energy required to refine a gallon of gasoline can be estimated based on the
energy content of crude oil and the refinery efficiency of the facility
performing the energy conversion; I can provide you a reputable source for both
values.
In a 2008 report, Argonne National Lab estimated that the efficiency for
producing gasoline of an "average" U.S. petroleum refinery is between 84% and
88% (Wang, 2008), and Oak Ridge National Lab reports that the net energy content
of oil is approximately 132,000 Btu per gallon (Davis, 2009). It is commonly
known that a barrel of crude oil generate approximately 45 gallons of refined
product (refer to NAS, 2009, Table 3-4 for a publication stating so). Thus,
using an 85% refinery efficiency and the aforementioned conversion factors, it
can be estimated that about 21,000 Btu -the equivalent of 6 kWh- of energy are
lost per gallon of gasoline refined:
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The documents referenced herein are publicly available, as follows:
Wang, M. (2008), "Estimation of Energy Efficiencies of U.S. Petroleum
Refineries," Center for Transportation Research, Argonne National Laboratory,www.transportation.anl.gov/modeling_simulation/GREET/pdfs/energy_eff_pet...
Davis, S., Susan W. Diegel, and Robert G. Boundy (2009), Transportation Energy
Data Book, edition 28, National Transportation Research Center, Oak Ridge
National Laboratory, cta.ornl.gov/data/
NAS (2009), Hidden Costs of Energy: Unpriced Consequences of Energy Production
and Use, The National Academies Press, www.nap.edu/openbook.php?record_id=12794&page=1
It is worth noting that refining one barrel of oil yields gasoline in addition
to other products, so only a portion of the refining energy used to refine a
barrel of crude is truly attributable to gasoline. Even so, in terms of energy
equivalencies, the preceding estimation is valid.
If I may be of further assistance, please do not hesitate to contact me. Your
interest in energy efficiency at the Department of Energy is appreciated.
Sincerely,
Jake
- Jacob Ward Program Analyst/PMF Vehicle Technologies Program Office of Energy
Efficiency and Renewable Energy U.S. Department of Energy
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