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September 20, 2012

Sierra Club Announces More Than 200 Million Oil-Free Electric Miles Driven

Electric car symbol cropped

The second annual National Plug In Day is September 23, 2012, and it marks an exciting milestone: over 200 million oil-free electric miles traveled in the U.S. This translates into 96.5 million pounds of carbon pollution that have not been spewed into the air (even taking into account emissions from electricity to charge EVs). It also means that consumers have avoided purchase of nearly 7.4 million gallons of gasoline and saved nearly $19.5 million dollars in fueling costs (comparing gasoline to electricity fueling costs).

MpgOur 200 million electric miles driven estimate is based on data we compiled on electric miles traveled by the Chevy Volt, and the Nissan Leaf, and Tesla Roadster models, as well as estimates on electric miles traveled by other recent plug-in vehicles, electric vehicle conversions, electric delivery fleets, and factory made electric vehicles prior to 2010 models. (See more on how we got to 200 million miles below.) From there, we determined the approximate avoided gallons of gasoline purchased, the money saved by fueling with electricity, and the pounds of carbon emissions prevented in comparison to a new compact car averaging 27 MPG.

How did we do this? First, let's look at avoided gallons of gasoline purchased.


How much carbon emissions would have resulted from those gallons? Each gallon of gasoline releases about 25 pounds of carbon pollution taking into account the approximately 19 pounds of carbon emissions per gallon from the burning of gasoline and is emitted from the vehicle tailpipe as well as the approximately 6 pounds of carbon emissions per gallon from the upstream emissions that are a result of the oil extraction, refining, and transport processes.

7,407,407.407 gallons X 25 pounds of carbon = 185,185,185.2 pounds of carbon

We're not done with this number yet. Next, we'll calculate the pollution associated with charging EVs and subtract that from the above to get carbon pollution avoided.

Because different parts of the United States have cleaner or dirtier grids, and because EVs are purchased and driven disproportionately in states with cleaner sources of electricity (like California), we wanted to make sure to count EVs, electric miles, and the emissions associated with EV charging based on where people are actually purchasing EVs. The Center for Automotive Research (CAR) report (pdf) for example, estimated that California EV sales would account for 24 percent of EV total EV sales in US in 2012.  So, we assumed that 24 percent of the 200 million electric miles were driven in California, and we determined emissions estimates accordingly.

For emissions, we look at the miles per gallon equivalent (MPGe) that a plug-in vehicle has in that state, as the Union of Concerned Scientists shared in their "State of Charge" report (pdf).

We calculate each state's charging emissions and add them up. Let's look at Massachusetts as an example, where CAR estimates that 3.1 percent of total US EV will take place in 2012. According to Union of Concerned Scientists, electric vehicles charged in Massachusetts have an estimated 75 MPGe.  This means that if someone charged and drove a Nissan Leaf in Massachusetts, it would be like driving a 75 mpg car in terms of its carbon emissions.

Projected EV miles driven in MA (3.1% of 200 million) / MPGe (75) = equivalent gallons of gasoline
((.031 X 200,000,000) / 75 = 82,666.67)  X  25 pounds of carbon = 2,066,666.67 equivalent pounds of carbon

We then did this calculation for all 50 states that total 88,685,066.87 pounds of equivalent carbon pollution emissions.


One caveat is that surveys have shown that a significant portion of EV drivers rely on solar power at their homes. While we didn't have enough data to factor this into our calculations, we know that with more solar in the mix, the amount of carbon emissions prevented is surely significantly higher than what we calculated.

Now we need to calculate the electricity costs associated with fueling EVs. We take the average electricity rates (cents/kWh) for each state and multiply by the efficiency of the vehicle to determine the cost per mile. We’ll use 0.34 kWh/mile as the efficiency. Using Illinois as an example:

9.13 cents/kWh  X  0.34 kWh/mile = 3.1042 cents/mile


Now we'll multiply this (3.1042) by the projected EV miles traveled in Illinois (0.038 X 200,000,000) and get 23591920 cents. Divide by 100 and Illinois EV drivers collectively spent a projected $235,919.20 to travel 7.6 million miles.

Add up all the states and together EV fueling for 200 million miles is $7,556,982.80.

So how we did we figure more than 200 million electric miles? Nissan informed us that as of July 31, 2012, Nissan Leaf drivers in the US had driven about 60 million miles. We estimated that an additional 5.9 million would be added by 9/23/12. We were able to obtain from the Chevy Volt web site that Volt drivers had driven 79,898,020 electric miles as of  9/16/12. We estimated that an additional 289,800 miles would be added by 9/23/12. From the Tesla web site, we know that Roadster drivers had driven 26,504,330 miles as of  9/16/12. Given that the vast majority of Tesla sales are in the US, we estimated just over 20 million miles have been driven by US Tesla drivers by 9/23/12. The total estimated electric miles among these three manufacturers were close to 166 million miles as of 9/23/12. We then estimated that among all the other new EV models starting to be sold and driven (plug-in Prius, Mitsubishi iMiEV, Ford Focus EV, BMW ActiveE, etc), all the thousands of vehicles that owners have converted from Internal Combustion Engines to EVs, all the EV delivery fleet vehicles (driven by companies such as Frito-Lay, Staples, FedEx, etc) -the total of this 'other' category is in excess of 34 million miles driven by 9/23/12 bringing us to a total of more than 200 million miles.

It adds up quickly, and this is only the beginning! More EVs are hitting the road, and our nation’s grid is continuing to get cleaner. A switch to EVs is significantly cutting our reliance on oil, our carbon pollution, and our fueling costs.

-- Gina Coplon-Newfield is the Sierra Club's Director of Green Fleets & Electric Vehicles Initiative, and Emmy Grace is an Intern with that program.


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