When Do Electric Cars Really Charge? All At The Same Time

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GE WattStation Electric Car Charging Station

GE WattStation Electric Car Charging Station

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If you’re not an electric car driver, the chances are that how and when electric cars recharge is one of the lesser mysteries of the universe. 

After all, if every electric car in town charged at the same time, wouldn’t it bring down the electrical grid? 

The answer, at least for now, is a resounding no.  But if electric cars take off, utility companies and electric automakers may have to work together to change the charging habits of electric car drivers to protect the gird. 

According to Scientific American, data collected over the past two months in Pecan Street, Mueller, TX, colloquially known as the world’s most concentrated neighborhood of Chevrolet Volts, shows that most electric car owners plug-in and charge the moment they get home, rather than charge their cars at night when grid demand is at its smallest.

The resulting spike in power, adding to the traditionally high demand period between 3pm and 8pm, means that the local utility company has to work harder to provide the necessary neighborhood with enough electricity.

Obviously, Pecan St. is not an average American neighborhood: it’s part of a new, green housing development being studied by the University of Texas at Austin. 

A3 e-tron charging station installation

A3 e-tron charging station installation

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But should this pattern of charging continue as electric cars become more popular, once electric cars are owned by 15 to 20 percent of residents in a particular neighborhood, those studying Pecan St. say utility companies could struggle to meet demand. 

That may sound like a nightmarish scenario, but for now, we're doubtful it will become reality.


First, because the 2012 Chevrolet Volt has a fairly limited all-electric range, it’s possible to drain the pack completely during an average daily commute. 

As a consequence, Volt owners are more likely to want to recharge when they get home, so their car still has enough all-electric range to do evening errands without relying on its on-board gasoline-powered generator. Most electric cars driven in the Pecan St. project are Volts, while wider communities are more likely to have a wide range of plug-in cars. 

By contrast, most 2012 Leaf owners will arrive home from the daily commute with plenty of mileage to spare, meaning they’re less likely to feel the need to charge immediately. 

Second, as a recent study by the Center for Sustainable Energy in California (CSEC) found out, as many as two-thirds of all electric car owners will charge their cars at night if utility companies offer appropriate incentives to do so. 

Power lines by Flickr user achouro

Power lines by Flickr user achouro

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In most cases, this means offering a special off-peak, or time-of-use rate that is cheaper than the usual day rate. 

With most electric cars on the market today offering built-in timers that allow owners to program their cars to charge at specific times, as long as utilities offer appropriate incentives, most owners will charge their cars at night while they sleep. 

With only 6 percent of all utilities in the U.S. offering time-of-use rates however, it may take some time before plug-in drivers take advantage of pre-programmed night-time charging.

There is of course, another solution: smart grid technology.

By allowing automakers and utility companies to work together through a smart grid, utility companies can let automakers know how much spare capacity exists in the electrical grid to charge electric cars at any one time. 

As General Motors has already demonstrated with its OnStar system, it  should then be possible to control when and how customers’ cars charge, preventing the kind of nightmarish scenario where tens of thousands of simultaneously charging electric cars bring down the electrical grid. 

For that to happen however, 15 to 20 percent of all cars on the road, equivalent to at least 1 million vehicles, would have to be electric. 

AND they’d have to all plug in at the same time. 

Given the number of electric cars on the roads of the U.S. isn't expected to top 1 million cars until at least 2015, we think automakers and utility companies have plenty of time to work on ways to encourage electric car owners to charge at night. 

Do you agree? Let us know in the Comments below.


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Comments (15)
  1. Interesting article, thanks Nikki -

    I'm not sure that Mueller Texas is a typical community for evaluating charging patterns. Mueller is atypical due to a high concentration of solar installed as well as having additional unique community renewable energy production. I believe the residents are familiar with their energy sources and I would bet that knowledge influences their behavior. Their thoughts might be "Hey, I've got PV on the roof I'm plugging in while the sun is high!". In addition, and as you state, there are no time of day energy consumption incentives.

    While I'm glad to see this type of information being gathered, I believe Mueller is really too small to be a good sample set (I think I ready they have 38 GM Volts).

  2. We have spent trillions on oil pipelines, drilling, transport, cleanup, and wars. Upgrading power grids will be pocket change.

  3. That can easily be changed if they offer "time varying" rate like you said. Even if 1 millions EV are on the grid with 40 miles daily driving, it will ONLY add additional 0.38% to the total US Electricity consumption.

    The Volt can be easily configured to plug in but charging at a much later time. With its fairly short range, its battery can be quickly charged within 4 hours at night.

    Even if it is charged, it is using fairly small amount of Electricity comparing with A/C, Electric oven/water heater.

    The Volt only draws 3.3KW. @ 240V, that is only 14 Amp. Electric stove (1.5KW per burner), oven (8KW), dryer(6KW), water heater (10KW) and A/C (11KW) all draw FAR MORE power than electric car charging. Charging the Volt on 120V, 1.5KW.

  4. Placing PVs in parking lots of work places where EVs will be parked for hours, doesn't hurt. This is a great opportunity for corporate America show how magnanimous and socially responsible they are to the community. We're talking pennies of investment for some corporations. They can start small by equipping a few parking spots and continue building based on long range plans. This effort will project a positive corporate image and encourage people to buy EVs. Corporations can even implement an employee/grant matching cost sharing scheme. I'm sure their accounting department can apply some of their creative and innovative talents to this effort that will eventually benefit the company and not financially hurt the employee.

  5. I am lucky that my work place has a 1MW solar system installed over the parking lot...

  6. You just made me think of something...the problem will not be people charging when they get home. Time of Use rates will make that problem go away - my super off peak rate is half the peak rate - I'd be a fool to charge when I get home from work. But there may be a problem with people plugging in at their employer when they get to work. I can see a surge in demand between 8-9am in the morning with millions of commuters plugging in.

  7. I still think the millions of commuters are still small potato in comparing with industrial usage that starts about 7 or 8Am in the morning...

  8. There are ways to solve these foreseeable issues while keeping the end user’s interest and original intents in mind. What about encouraging the development of home power storage units that store solar energy during the day for homeowners evening usage? Or placing PVs at the workplace, as suggested earlier? There have been some innovative breakthroughs in recent years. The problem is that these innovations are often blocked by the very companies that feel threatened by them.

  9. YElectric car users should follow the lead of solar homeowners; power the home by solar during the day, and feed any excess back into the reverse meter (available in 40 states) which will credit the homeowners utility bill at the going rate for the time of day.
    Electric car owners could similarly charge their car at midnight (on timer, paying about $.05 KWh). The next evening, after day's driving is done, they would feed whatever juice is left (down to 10%) back into the meter in reverse, getting credit at the time of day rate (say $.15). A carefull driver with a modest commute might even make a profit!ou must be logged in to post your comment.

  10. Interesting idea. The utilities seem to be fighting hard to prevent competition and your scheme would be possible if the laws are changed to allow renewable energy to be sold back to the utilities at the prevailing market rate.

  11. Whoops. I hit "bad stuff" by mistake on my own comment and there is no undo button.

  12. BS scare tacicks buy the oil co.

  13. It's a shame we have to put up with all this crap about how the EVs will overload the grid while so much energy is being wasted on nothing. In 2010, according the the Edison Energy Efficiency Institute, efficiency programs saved 112 TWH. I can drive my LEAF over 400 billion miles on that much energy. 400 billion miles is approximately 13% of the total miles driven in 2010. So, just in one year through conservation, we saved enough to cover millions of EV's power needs.

    Before we get our panties in a bunch over EV power use, we should get serious about efficiency.

    How many miles can we drive on the energy used by people watching junk TV? How many miles can we drive on the energy used by people using hair dryers?

  14. Exactly, I did a quick math the other day with the figures from EIA. The amount of electricity consumed for 40 miles commute by 1,000,000 EVs will only add 0.38% load to the entire US grid. That is 1 Million EVs. We are NO where close to that. That doesn't include the power saved from less refinery usaged due to the gas saved. 1,000,000 ICE cars driving 40 miles per day would use about 1,000,000 gallon of gas per day...

  15. Until the utilities adopt time of usage rates, this problem is unlikely to improve. I spoke with the Manager & Board of Directors about time of use metering at my electrical distributor and they say there are too many problems with TOU meters for them to justify implementation. Even if the problems did not exist, they say on their margin, they can't afford to buy the meters and change them out without raising everybody on their systems rate by about $76.00 per month.

    I have no way of knowing how much of that is fact and how much is padded figures, but either way, they won't play. If they won't play, many people will plug in as soon as they come home so they can go about their normal routine.

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