Plug-In Vehicles and the Power Grid

By Kevin Miller


2011 Chevrolet Volt Production Show CarAs evidenced by the slew of electric and plug-in-hybrid vehicles seen at NAIAS this week as well as in LA last month, zero-emission plug-in electric vehicles (PEVs) will soon be silently whirring into driveways and garages near you. While the fallacy of calling these vehicles “zero emission” won’t be addressed here (other than a note that you’re fooling yourself if you think the coal-fired power plant generating your electricity is “zero emission”), the impact on the electric distribution network that recharges those PEVs will.

At last month’s LA Auto Show, California’s regional electric utility Southern California Edison (SCE) had a booth and representatives for the purpose of informing consumers about their options for variable rate plans for recharging their PEVs, and also asking customers to let their utility know when they’re planning to install a PEV charger at their residence.

While it is admirable that utilities such as SCE are preparing for the additional loads of PEVs, some critics believe the utility is putting its proverbial cart ahead of its horse. As Autosavant reported almost three years ago, a 2006 study by the US Department of Energy study determined that the nation’s existing electrical grid has enough capacity to accept the addition of 180 million plug-in vehicles. That is a really big number; consider that about 10.4 million new vehicles were sold in the US in 2009, so it would take at least 15 years for our country to reach 180 million vehicles, and that is assuming that every car sold has plug-in capability, which it won’t. So you might ask why utilities are so worried about the additional electrical load coming from PEVs? There are a few reasons.

leaf_chargeportsToday, when you go out and buy a new car, you can take it off the dealer’s lot and drive it around for hours, showing it off to all of your friends and carving your favorite canyons in an ecstatic state. You know that when you get low on fuel you can drive it to the nearest filling station and buy more. With an electric vehicle, it isn’t quite that easy. If you haven’t installed the charger at your house before you bring the EV home, you aren’t going to have very much fun with it, as it’ll be out of juice and you’ll have no way to recharge it. Even if the car can plug in directly to an electrical outlet without needing a separate charger, many garages will need to have the appropriate electrical receptacle installed in order to be able to plug the vehicle in.

So the first tenet of SCE’s PEV awareness campaign is to make customers aware that they need to make their garages ready for their EV purchase by having a charger or receptacle installed. The type of existing electrical service in the home will determine whether upgrades to the home’s service are required, and will also dictate the supply voltage to the charger, which will have an effect on charging time if the home doesn’t have the desired voltage or current available. It may take a week or more to arrange to have the charger and any associated circuits installed by an electrical contractor and have the necessary inspections take place, so it’s a good idea to do that before you bring the car home.

2010 Toyota Prius Hybrid plug-in - lease trial vehicleThe second tenet of SCE’s campaign is to inform customers of different rate plans available based on power usage and the time of day people choose to charge their PEVs.One of the challenges that any electric utility faces right now is that they have no way of knowing just how high the demand will be for PEVs. If relatively few consumers buy the cars, their effect on energy consumption in a distribution grid will be negligible. However, if a lot of people buy PEVs, and all charge them at the same time, the electric distribution grid may become overloaded, causing brown-out or power loss in certain areas. To understand why this might happen, let’s take a quick look at the typical electrical supply grid for a neighborhood.

Electricity is transmitted from power plants (whether those are coal-burning, hydroelectric, wind, solar, or other) to substations at a high voltage. At the substations, the electricity is stepped down to “medium voltage”, where it is distributed to neighborhoods. Neighborhoods have transformers which step the voltage down further; a typical neighborhood has perhaps six to ten homes supplied by a such a transformer. You’ll see the transformer either as a cylindrical metal thing up on a power pole, or in a squarish metal box sitting on the ground with HIGH VOLTAGE warning stickers all over it.

Volvo C30 ElectricNeighborhood transformers are sized to supply an average neighborhood with typical power usage. In Southern California, those transformers are able to accommodate homes with air conditioning or heating, electric cooking appliances, and electric clothes dryers. Assuming that the PEV charger has the same approximate current draw as an average air conditioner (somewhere around 220-240 VAC, 3 kW), adding one or two PEVs to a neighborhood won’t likely be a problem for the distribution system. However, if every house on the block ends up with a PEV and they all charge at the same time of day (especially if other large electrical loads are operating at the same time), the possibility exists that supply circuits could become overloaded, leading to a brown-out or power failure condition. By contacting the utility ahead of time, SCE’s goal is to be able to upgrade their distribution network at the neighborhood level where needed, so that power delivery is seamless and uninterrupted.

Of course, the rate of power usage in in our society not static, but instead is dynamic. Most power is used during the day, when people are working; their computers or tools are running, as are air conditioners or heaters in offices, stores and homes. After work, the load switches to HVAC, cooking, laundry, and entertainment. Finally, when people go to sleep and turn off the lights, energy usage falls to its lowest level of the day. That being the case, SCE would like to encourage PEV owners to recharge their cars overnight instead of mid-day. to that end, they have implemented different electric rate structures which make it less expensive to recharge vehicles during off-peak hours.

While the overall power grid is capable of supporting the addition of plug-in vehicles, neighborhoods and homes may require upgrades to facilitate charging those vehicles. A PR campaign on the part of electric utility providers serves the purposes of letting the customers know what steps they should take to prepare for a plug-in vehicle purchase, and also encourages the customer to let the utility know when they are going to purchase a PEV, so the utility can proactively upgrade their neighborhood distribution system if required.

COPYRIGHT Autosavant – All Rights Reserved

Author: Kevin Miller

As Autosavant’s resident Swedophile, Kevin has an acute affinity for Saabs, with a mild case of Volvo-itis as well. Aside from covering most Saab-related news for Autosavant, Kevin also reviews cars and covers industry news. His “Great Drive” series, with maps and directions included, is a reader favorite.

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  1. In Arizona prety much everyone is on a “time of use” plan. Daytime electricity might cost 12 cents per KW/hr, where nighttime electricity is 3 cents.

    I can’t imagine anyone intentionally charging a PHEV or PEV on daytime rates when a $5 timer would alow you to charge at 1/4th the cost.

  2. At this point, is there any average cost per mile for electric vehicles? Not hybrids because the cost per mile is pretty variable depending on the gas engine also in the car, but a pure EV. Is there an average cost per mile?

  3. That’s a good question. What is the average cost per mile of an electric vehicle?

  4. The question of cost per mile is a good one. It is a function of both the electrical efficiency of the EV, and how much electricity costs where you live. With electricity costing $0.15/kWh, cost per mile would be between 3 and 8 cents/mile. At $0.25/kWh, cost per mile climbs to 5-12 cents per mile, again depending on efficiency of the EV.

    As a comparison, a car with average 22 MPG and $3/gallon gasoline price costs about 13 cents/mile.

    I found this data from the Idaho National Labs’ Advanced Vehicle Testing website,, and didn’t spend a lot of time looking at their methodologies, so I’m only offering those numbers as an approximation.

  5. Cost-per-mile is a lot more accurate measure for any hybrid as well, since the preliminary MPG ratings of some of the upcoming hybrids are just astonishing.

    The problem for doing this with a hybrid is that cost-per-mile goes up from the time of purchase if the price of gasoline rises. It seems the price of kw is a lot more stable, even if there is considerable variance between regions or metro areas.

  6. It’s going to be a long time before hybrids or electrics make sense from an economic perspective. The current payback period for the average hybrid is around 15 years.

    For it to be 3 years, which is where consumers want it, everyone agrees more of less that the cost of electricity used has to get to the $250 per KW/hr standard as used by an electric vehicle. That includes everything. the cost of the vehicle, the cost of the electricity, maintenance, etc. Everyone is a long, long way from that right now.

    Here is some of the press release concerning potential payback time from Boston Consulting Group put out last week:

    “Consumers want a three years or less payback period for the extra cost of the batteries,” said Massimo Russo, a partner in the Boston office.

    BCG expects the cost of a 15-kWh ranger extender pack will drop from about $16,000 now to about $6,000 in 10 years, and consumers could still be expected to pay as much as $10,000 extra for electric vehicles at that rate.

    And a decade from now, it is unlikely there will be a $7,500 tax credit to soften the blow, Mosquet said.

    For consumers to break even on their electric car purchase, one of the following things must happen:

    There is a chemistry breakthrough that keeps material costs the same while creating a battery that can store twice as much energy, reducing the cost from $400 per kW/hr to $215.

    A new $7,700 government incentive is offered.

    Owners triple the number of miles they drive annually so the extra cost pays for itself.

    Oil prices increase from $100 a barrel to $375 a barrel.

    A 210 percent incremental gasoline tax is implemented.

    While any of them are possible, or a combination of each could add up to enough, Mosquet said he sees it as unlikely. As a result, he expects electric vehicles will continue to play a minor role in most automakers’ portfolios.

    Everyone’s got their own opinion which one of those things (or combination of partial things) is most likely to happen in the next 20 years, but I think it’s very clear that that chances of any of those things, excluding the tax credit, happeing in the next five years is extremely low.

    Think about that before you consider an electric vehicle.

  7. Oil at $375 a barrel would mean most purchasing by consumers would grind to a halt since that would affect a lot other things besides the price of gas, so it’s probably a moot point about how many electric cars would be bought. Maybe after the Second Great Depression was over, people could buy electric cars.

  8. If these connections are the same as a W\D connection, it would seem the utilities are being very cautious, indeed.

    If you think about the average suburban street, there are a lot of washers and dryers operating at the same time, with hair dryers, power saws, electric hedge trimmers, and all sorts of other things in the mix at the same time. Is this going to put that much more load on the very local grid there?

    Plus, almost every car would be recharged at night. Plus, not that many people would have an electric car or a plug-in hybrid on the street.

  9. Those numbers on payback for EV are sobering, but I’m thinking that it will be a combination of perhaps all of those things changing a little, as opposed to one thing changing enough by itself to make the payback time fall into line.

  10. What if you live in a city and want an EV? Will the utility companies be putting in charger outlets along the curb?

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