The “State of Charge” of Electric Vehicles: Good and Getting Better

, research and deputy director, Clean Vehicles | April 16, 2012, 1:10 pm EDT
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Today UCS released State of Charge, a new report on electric vehicles that gives a snapshot of the global warming benefits and fuel costs savings that this technology currently offers. The results are in, and the news is positive. Electric vehicles (EVs) are a good choice for lowering global warming emissions from driving, no matter where in the U.S. you live, and driving on electricity can save drivers upwards of $1,000 per year in fuel costs.

Some of you EV enthusiasts out there may have noticed that the title “State of Charge” is a reference to electric vehicles. The “state of charge” of your EV tells you how much juice you’ve got in your batteries just like a fuel gauge tells you how much gasoline you’ve got left in your tank. But the name also implies that the results are a snapshot of the current moment, and that the state is subject to change.

2012 Ford Focus Electric (Copyright Ford Motor Company and Wieck Media Services, Inc.)

So, what’s today’s “State of Charge”?

Nearly half of Americans live in regions where driving on electricity is better for global warming emissions than driving the best gasoline-powered hybrids available today. Even in the regions of the country where coal dominates the electric grids, EVs emit global warming emissions similar to the best compact conventional gasoline vehicles – those averaging between 31-40 mpg.

Across 50 of the largest U.S. cities, EV owners can  save $750 to $1,200 on fueling costs each year compared to the average new compact gasoline vehicle filled up at $3.50 a gallon.

And, of course, driving on electricity slashes oil consumption.  Not only are you avoiding trips to the gas pump, very little of the nation’s electricity is generated with petroleum. Less than 1 percent in fact.

This is all good news. But the future for EVs can be even better.

Our current transportation fuel supply is nearly all petroleum.  Our electricity grid, on the other hand, is powered by a variety of energy sources, from coal and nuclear to wind, solar, and hydro. By plugging our cars into the grid, and working to reduce the amount of dirtier electricity sources like coal and increasing renewables like wind and solar, we can clean up both our transportation and electricity sectors at the same time.

The move to a cleaner grid is underway; 29 states and Washington D.C. have standards in place to accelerate the transition to cleaner electricity, and projections for new coal plants have been declining while older coal plants are being retired.

As a result, an EV bought today can actually be expected to get cleaner the longer you own it.

This cannot be said for our oil-powered cars.  New gasoline vehicles burn less fuel on average than older vehicles, and will continue to improve over the next decade thanks in part to new fuel economy and greenhouse gas standards. But the gasoline itself is likely to get dirtier as we depend more on harder to extract oil like Canada’s tar sands and dirtier sources of crude oil. As a result, a gasoline vehicle is likely to emit more emissions per mile as it gets older.

Charging Forward

Our report shows that the State of Charge is strong, and that EVs can play a significant role in reducing air pollution, global warming, and oil use. If we continue to support innovation and infrastructure investments to make EVs more affordable and easier to own for more consumers, the market for EVs will grow. And continuing to clean up our electricity grid will ensure that the full climate benefits of electric drive vehicles are realized everywhere in the United States.

Getting more EVs on the road will take time. As we note on our Model E website, the transition from oil-powered transportation will be an evolution rather than a revolution, but working together we can continue to power up a clean EV future.

To support cleaner energy and cleaner vehicles in your city or state, take action today.

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  • Keith

    I really wish you had addressed the use of natural gas as a fuel in your report. I see a strong movement developing that is pushing nat. gas as an alternative to EVs. And while nat. gas does make sense for some applications (trucking, fleets), its deployment for personal transport would set back EVs for decades.

    Yet, there is no concrete analysis comparing the cost benefits of EVs over nat. gas vehicles, when those of us with science background fully understand that “near zero” emissions from nat. gas vehicles is not the same as no emissions.

  • Josh Bryant

    Don, I liked the purpose of the “State of Charge” report, but there were two key mistakes I can see in the numbers used.

    First, the energy generation data used is from 2007. There has been significant change in the energy content on the grid in the last 5 years. Massive adoption of natural gas and significant capacities of wind throughout the Midwest. Full disclosure, I work in the wind industry, so I follow these trends closely.

    The second inaccuracy is the efficiency of the Nissan LEAF used as the baseline vehicle. I can see how the calculation was made 24 kWh battery / 73 miles range (EPA). In actually the LEAF only uses 21 kWh’s of the pack and the miles per kWh average about 3.5 miles / kWh, or .28 kWh / mile as you are using it. I can verify this as I drive my LEAF 66 miles round trip everyday 80% highway (70 mph). Some drivers with more city driving average closer to 4.0 miles / kWh and probably could achieve the “100 miles range” Nissan claims. For my driving, I find the EPA rating much more accurate.

    Any chance an update to the report could be done with new numbers. It would paint a more accurate, positive picture on where we are today. I want to reiterate that I totally support the purpose of the report and the method in which it was done.

    Thanks for your work.

    • Thanks for your comments Josh. I agree the electricity grid has been getting cleaner since 2007 for the reasons you point out. We used the most recent data available from EPA’s eGRID database, which consolidates power plant emissions data into the regional grids. As new data is released, we will update our analysis and we expect to see a trend in the right direction based on greater renewables, coal plant retirements, and greater investments in natural gas. As we note in the analysis, an EV purchased today can be expected to get cleaner as it gets older.

      To your second point, we do in fact use the EPA efficiency rating of the Nissan LEAF for combined city and highway driving, which is 0.34 kWh/mile. This figure includes the charging losses which might explain the differences you note. If you just look at how efficiently the LEAF converts the energy stored in the batteries into miles traveled, you end up with a better efficiency number. But to determined the actually electricity consumed by the vehicle, you need to include the charging losses as well.

      Hope that helps. Thanks – Don

  • Kimbal Sundberg

    We bought a 2012 Chevy Volt to replace our faithful 17-yr Saab in December. Here on San Juan Island, WA, where our utility purchases 95% renewable (mostly hydro)and charges 7.8 cents / kwr, it costs about 95 cents to “fill up” the battery. This is equivivalent to 3.5 cents per mile. That’s opposed to paying $4.65 / gallon for gas at the pump or 23 cents per mile for the Saab. We run 100% electric (zero emissions) on the Island and burn gas (about 35 mpg) for longer trips to the mainland. After 2,600 miles, our Volt has burned 30 gallons of gas and is averaging 81 mpg. As retired habitat biologists, travel enthusiasts, and long time UCS members, owning a Volt is a no-brainer. We just hope the truth about the Volt gets out (despite the right-wing / oil lobby disinformation). Once you own one, you wonder why there aren’t more being sold.

    • Thanks for your comment Kimbal. Your experience highlights a number of benefits of driving on electricity instead of gasoline. Our national analysis of emissions uses the regional mix of electricity to estimate the emissions from charging an EV. As your experience shows, you may be able to do better than the average if your local utility invests in greater amounts of renewables than their counterparts. Many early electric vehicle owners are also opting to generate their own electricity with rooftop solar for example. Utilities have a big role to play in supporting increased renewable electricity. Some offer optional programs for their customers to choose greater renewable power which is good. Even better is increasing the amount of low-carbon renewables into their mix of electricity sources so all of the customers they serve will get cleaner electricity.

      • Kimbal Sundberg

        Your report is a good first step in quantifying the well to wheel costs of operating EVs. It is a valuable contribution to helping the public make informed choices about purchasing new vehicles. As one who has worked a lifetime in natural resources conservation and currently volunteers in salmon restoration, I always wonder about the true costs of “clean energy” including hydro and nuclear. Because of its abundant fresh water resources and Federal investments, our region has access to relatively cheap hydroelectric energy. This has come at great cost to salmon runs, other natural resources, and indigenous people. Fortunately, nuclear energy virtually died in the Pacific NW during the 80’s due to bond scandals and cost overruns. However a massively expensive Federal nuclear waste clean up continues at Hanford. Hopefully your paper will spur you and others to quantify the true costs of “clean energy”. In my mind, using less energy and having fewer people is the path to solution.

  • Adrian Gross

    The study specifically mentions that it wants to compare apples to apples and take into account the whole chain from well to wheel. However, I saw no data on the GHG emissions involved in the production and transportation of gasoline. Did I miss it or is it just not there? It is commonly estimated that the refining of a gallon of gasoline costs about 5 kWh of energy (not all of it electric). Where in the data is this accounted for?

    • Thanks for the question Adrian. The study does in fact account for the extraction, refining and transportation of gasoline. We used Argonne National Labs GREET model which shows that inclusion of these “upstream” emissions adds about 25% to the emissions from the tailpipe. We also included the emissions from extraction and transportation emissions of energy sources used in electricity production. For example, the emissions from coal mining and transporting the coal to the power plant are included. Hope that helps to clarify.