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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 
Quantity of gasoline produced - EIA - Petroleum & Other LiquidsManufacturing Refining  
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:

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.



- Jacob Ward Program Analyst/PMF Vehicle Technologies Program Office of Energy Efficiency and Renewable Energy U.S. Department of Energy