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Energy, Infrastructure, Sustainability, Transportation

Reducing U.S. gas consumption: Plug-in hybrids versus charging infrastructure

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Research has shown that, as with many things in life, the devil is in the details when comparing the efficiency of conventional and hybrid cars. When an automobile generates all its own power — as with those that run on fossil fuels — it’s simply a question of aiming for one with the highest possible gas mileage. Things get trickier with plug-in hybrids, however: Is the power they get from the grid produced by state-of-the-art solar farms, or down-and-dirty coal plants? It depends on where you plug in.

Things are trickier still when considering the potential benefits of a large-scale network of car-charging stations across the United States — infrastructure that doesn’t yet exist. While such a network would allow wider adoption of plug-in hybrids and all-electric cars, would building it lead to lower environmental costs than current gas-electric hybrids?

A 2013 study published in Energy Policy, “Cost-effectiveness of Plug-in Hybrid Electric Vehicle Battery Capacity and Charging Infrastructure Investment for Reducing U.S. Gasoline Consumption,” looked at the relative benefits of a vehicle-charging network and hybrid vehicles with larger batteries. The researchers, based at Carnegie Mellon University, examined gas and power consumption by plug-in hybrid electric vehicles of varying battery capacities and under a range of charging-infrastructure scenarios.

In the study, the researchers note that a number of financial incentives are in place to encourage the adoption of cleaner vehicles: The U.S. government has given grants of $137 million for the installation of approximately 18,000 charging stations in select areas; and buyers of hybrid electrics get a tax credit of $2,500 up to $7,500 based on battery capacity, not vehicle range. This extra capacity isn’t without cost, as larger batteries weigh more, cutting into the additional range theoretically available.

The study’s findings include:

  • Across the battery-capacity and charging-infrastructure scenarios examined, the lowest-cost solution is for more drivers to switch to traditional hybrid electrics or low-capacity plug-in hybrid electric vehicles (PHEVs): “Charging infrastructure is generally not necessary for operation of PHEVs and substantial gasoline displacement can be achieved solely with home charging.”
  • Installing charging infrastructure would provide lower gasoline savings per dollar spent than paying for increased PHEV battery capacity: “We find that the maximum cost per gallon saved for increased [all-electric range] is 5% to 40% less than the minimum cost per gallon saved when installing charging infrastructure, depending on vehicle class.”
  • “Looking forward as battery prices decrease and the [all-electric range] resulting in maximum lifetime cost savings increases, the relative value of plugging in multiple times throughout the day will also decline.”
  • “The limited range of BEVs [battery electric vehicles] make nondomestic charging infrastructure more critical if the vehicles are to be used as primary vehicles. But public investment in either large-battery vehicles or charging infrastructure generally produces fewer benefits per dollar spent than investment in small-battery PHEVs.”

The researchers conclude: “It is clear that federal subsidies are not currently aligned with the goal of decreased gasoline consumption in a consistent and efficient manner. Other relevant policy objectives, including reduction of emissions externalities, encouragement of technology development, and job creation do not show clear benefits of favoring large battery packs over small battery packs.”

A related study, “Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles,” analyzes how electric cars stack up against those with traditional gas and diesel engines over their entire life cycle.

Tags: cars, renewable energy, technology, fossil fuels, infrastructure

    Writer: | Last updated: March 14, 2014

    Citation: Peterson, Scott B.; Michalek, Jeremy J. "Cost-effectiveness of Plug-in Hybrid Electric Vehicle Battery Capacity and Charging Infrastructure Investment for Reducing U.S. Gasoline Consumption," Energy Policy, January 2013, Vol. 52, 429-438. doi: 10.1016/j.enpol.2012.09.059.

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    Analysis assignments

    Read the issue-related New York Times article titled "Budget Shortfall Could Imperil Subsidies for Electric Vehicles."

    1. What key insights from the news article and the study in this lesson should reporters be aware of as they cover these issues?

    Read the full study titled "Cost-effectiveness of Plug-in Hybrid Electric Vehicle Battery Capacity and Charging Infrastructure Investment for Reducing U.S. Gasoline Consumption."

    1. What are the study's key technical terms? Which ones need to be put into language a lay audience can understand?
    2. Do the study’s authors put the research into context and show how they are advancing the state of knowledge about the subject? If so, what did the previous research indicate?
    3. What is the study’s research method? If there are statistical results, how did the scholars arrive at them?
    4. Evaluate the study's limitations. (For example, are there weaknesses in the study's data or research design?)
    5. How could the findings be misreported or misinterpreted by a reporter? In other words, what are the difficulties in conveying the data accurately? Give an example of a faulty headline or story lead.

    Newswriting and digital reporting assignments

    1. Write a lead, headline or nut graph based on the study.
    2. Spend 60 minutes exploring the issue by accessing sources of information other than the study. Write a lead (or headline or nut graph) based on the study but informed by the new information. Does the new information significantly change what one would write based on the study alone?
    3. Compose two Twitter messages of 140 characters or fewer accurately conveying the study’s findings to a general audience. Make sure to use appropriate hashtags.
    4. Choose several key quotations from the study and show how they would be set up and used in a brief blog post.
    5. Map out the structure for a 60-second video segment about the study. What combination of study findings and visual aids could be used?
    6. Find pictures and graphics that might run with a story about the study. If appropriate, also find two related videos to embed in an online posting. Be sure to evaluate the credibility and appropriateness of any materials you would aggregate and repurpose.

    Class discussion questions

    1. What is the study’s most important finding?
    2. Would members of the public intuitively understand the study’s findings? If not, what would be the most effective way to relate them?
    3. What kinds of knowledgeable sources you would interview to report the study in context?
    4. How could the study be “localized” and shown to have community implications?
    5. How might the study be explained through the stories of representative individuals? What kinds of people might a reporter feature to make such a story about the study come alive?
    6. What sorts of stories might be generated out of secondary information or ideas discussed in the study?