HomeMy WebLinkAboutRelative “Greenness” of Electric Vehicle Technology 10-26-2010 -rpt
W. Levison/P. Levy 10/26/10
Relative “Greenness” of Electric Vehicle Technology
A question has arisen as to whether the introduction of electric (battery-powered) vehicles (EV)
may be legitimately considered “green” technology compared to an automobile powered by an
internal combustion engine (ICE). This simplified analysis considers “greenness” in terms of
carbon dioxide emissions.
The analysis proceeds as follows:
1.Compute kWh of battery power to drive a representative EV one mile.
2.Consider charging efficiency to compute kWh from the electric grid to drive 1 mile.
3.Compute the kWh per mile provided by the major CO generating energy sources.
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4.Compute the pounds/mile of CO generated by the various energy sources to yield the total
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pounds/mile of CO.
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5.Compute the number of miles/gallon required of a vehicle powered by an ICE to match the
EV CO production.
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Computation of Emissions for Electric Vehicles
The Nissan Leaf is considered here as representative of pure battery-driven electric vehicles, and
the Chevrolet Volt as representative of a plug-in hybrid vehicle.
Full battery charge is 24 kWh.
http://nissan-leaf.net/2010/05/27/nissan-leaf-battery-specifications/
Range is stated as 100 miles for city driving based on EPA LA4 test cycle. Can vary from 47 to
138 miles depending on conditions. Assume 100 miles for analysis.
http://en.wikipedia.org/wiki/Nissan_Leaf
This yields 0.24 kWh/mi from the battery.
Assume 87.5% charging efficiency
http://www.dailytech.com/Tesla+CEO+Calls+Nissans+Leaf+Battery+Tech+Primitive+Boasts+
About+Model+S/article19286.htm
This yields 0.24/.875 = 0.274 kWh/mi from the power grid.
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W. Levison/P. Levy 10/26/10
Electric Generation by Energy Source 2009 (thousand megawatt hours):
Source kWh Fraction
Coal 1,764,486 0.446
Petroleum liquids 25,792 0.007
Petroleum coke 13,035 0.003
Natural Gas 920,378 0.233
Other gasses 10,698 0.003
Nuclear 798,745 0.202
Hydro 272,131 0.069
Other renewable 141,115 0.036
Hydro pumped storage -4,346 -0.001
Other 11,078 0.003
Total 3,953,112 1.000
http://www.eia.doe.gov/cneaf/electricity/epm/table1_1.html
kWh/mi from individual sources is:
Coal: 0.446 * 0.274 = 0.122
Natural gas: 0.233 * 0.274 = 0.064
Petroleum: 0.010 * 0.274 = 0.003
Nuclear 0.202 * 0.274 = 0.055
Hydro 0.069 * 0.274 = 0.019
Pounds of CO per kWh emitted by the above energy sources (1998) are:
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Coal: 2.12
Natural Gas: 1.31
Petroleum 1.92
Nuclear 0 (assumed)
Hydro 0 (assumed)
http://www.eia.doe.gov/electricity/page/co2_report/co2report.html
Pounds of COemitted per mile attributed to each energy source are:
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Coal: 2.12 * 0.122 = 0.259
Natural Gas 1.31 * 0.064 = 0.034
Petroleum 1.92 * 0.003 = 0.006
Nuclear 0 * 0.055 = 0.000
Hydro 0 * 0.019 = 0.000
This totals to approximately 0.3 pounds/mile of CO emitted for the Nissan Leaf.
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The Chevrolet Volt is capable of travelling 25-50 miles on a fully-charged 16 kWh battery, with
an expected all-electric range of 40 miles under normal driving and climate conditions.
http://en.wikipedia.org/wiki/Chevrolet_Volt.
With a range of 40 miles and an assumed charging efficiency the same as for the Leaf, the Volt
uses (1/0.875)*(16/40) = approximately 0.457 kWh/mi from the power grid.. Extrapolating from
the Leaf computations, we compute (0.475/0.274) * 0.3 = approximately 0.5 pounds of CO
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emitted per mile.
Comparison to internal combustion engine
1 gallon of gasoline yields 19.4 pounds CO
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http://www.epa.gov/oms/climate/420f05001.htm#calculating
Gallons of gasoline to yield 0.3 lb CO = 0.3/19.4 = 0.0155
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Equivalent miles/ gallon = 1/.0155 = approximately 65 mi/gal for the Leaf in favorable driving
conditions.
Now assume the least favorable driving conditions tested; e.g., heavy stop-and-go traffic
averaging 6 mi/hr with the climate control in use. In this case the EV range is 47 miles. The
equivalent miles/gallon for a gasoline-driven engine is 65*(47/100) = approximately 31 mi/gal
for the Nissan Leaf.
Gallons of gasoline to yield 0.5 lb CO = 0.5/19.4 = 0.0258. The equivalent mi/gal for an ICE is
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approximately 39 mpg for the Volt under favorable conditions.
For the least favorable conditions considered (25 mile range), the equivalent gas mileage would
be (25/40) * 39 = 24 mpg.
The CAFE standards call for an average of around 35 mpg for cars and light trucks by 2016.
http://www.nhtsa.gov/Laws+&+Regulations/CAFE+-+Fuel+Economy/Model+Years+2012-
2016:+Final+Rule
If we assume that this requirement will actually be achieved by ICE vehicles, the foregoing
analysis does not conclusively establish that electric vehicles will be “greener” than ICE-
powered vehicles in term of CO production. Both the Leaf and Volt show greater equivalent
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mileage (i.e., less pollution) under favorable conditions, but less equivalent mileage under
unfavorable conditions. These are not totally fair comparisons, however, because a presumed
average ICE mileage was used. A fairer comparison would be between electric and ICE vehicles
operating under the same conditions.
A more thorough comparison of the environmental impacts of electric versus ICE vehicles would
consider factors such as:
Comparisons of EV and ICE vehicles under a variety of driving conditions with some kind of
averaging over these conditions.
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Other vehicle emissions (especially greenhouse gases).
Environmental concerns associated with electric generation other than CO emission such as
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nuclear waste disposal and the effects of dams built for hydroelectric generation on fish and
other wild life populations.
The extent to which carbon sequestration from coal-burning plants may become
economically viable.
Pollution associated with manufacture and disposal of EV batteries.
Pollution associated with the extraction, transport and refining of the raw energy sources.
The likely mix of energy sources used in generating electricity in the future.
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