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How to Solve an Electric Car-Charging Problem? Ask Our Readers


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What would happen if thousands of people in an average city eventually bought electric vehicles, and they all tended to plug in their cars for recharging during the same time of day? The spike in electricity demand could force the local utility to turn on an expensive backup power plant to generate the juice, and could even lead to a brownout.

It turns out that such a problem is not just theoretical. Data about the recharging habits of electric cars owners living in a new, 280-hectare neighborhood in Austin, Tex., known as Mueller, show that across two months time, the residents all tended to plug in their cars in the early evening when they came home from work. And that’s just when many residents are also turning up their air conditioning and turning on lights, TVs, computers and other appliances.

A few weeks ago I posted an article about the test results. Since then readers have added more than 40 comments to the story, a number of which include smart ideas about how to spread the demand for recharging cars across a day. Some of the most intriguing comments, edited for length, are below. Feel free to add to the conversation at the original article.

Why not have the [home car] charger on a timer so that it activates in off-peak hours, say after midnight? The battery would still be fully charged by morning without impacting the power grid during peak hours.

They *could* delay the charge until after midnight, but there’s no incentive for them to do so, since rates for electricity use at midnight are the same as at 6 p.m. Currently some utilities ask customers to voluntarily install a remote shut-off in case of brownouts. In return they get a deal on their rates. Why not offer electric car owners discounted evening rates if they install a delay switch?

Rock LeBateau
In the U.K. we used to have an “economy 7” tariff for electricity. It ran for seven hours from midnight, and was measured on a separate meter. People used to run their dishwashers and their washing machines and tumble driers on it. The electricity board used to sell the electricity at a discount because it was at a time when demand was at its lowest, and extra power could be produced cheaply on under-utilized generating capacity. You can modify customer demand using price.

Interestingly enough, time of use rates can sometimes create as many problems as they solve. If you look at the reports from The EV Project, in regions where time-of-use rates are effective, there is a bunching of vehicles charging at midnight, when time-of-use rates kick in. The central generating plants are just fine as the demand is predictable, but the local transformers are where any problems may show up. What is needed is smart grid technology when the vehicles and other appliances can be scheduled to draw current using minute-by-minute pricing information from the utilities, such that demand can be smoothed out and costs to the consumer minimized.

Tesla Motor’s electric vehicles come complete with touchscreen and smartphone charge scheduling. Owners can simply plug in after parking and the charging begins at the programmed time.

Use two-stage charging. Overnight, wall outlet builds up the charger—trickle charge takes longer but adds less load. The charger plugs into the car anytime.

We in Spain have a special energy tariff to promote electric vehicle recharge during non-peak hours (at night, when the car tends to “sleep” and when wind energy production increases).

Ross Nicholson
Electric cars can carry solar panels and be parked and driven in the sunshine.

Park at work, charge at work. Go to the mall for four hours, charge for 4 hours. Get a 2.5 hour charge at the cinema. [Of course, this requires public charging stations.]

I own a Volt. The Volt does have a timer that lets me charge after 8 p.m. (off peak). The reason I program the car to charge after 8 p.m. is that my charger is on a separate “time of use” meter and it is 1/4 of the price for me to charge after 8 p.m. All EV’s sold today do have a delayed charge feature.

Photo courtesy of Rob Fruth on Picasa Web



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  1. 1. Dzhafer07 4:43 pm 09/12/2012

    Naked Science
    Principled action of inventions that will change the world and scientific article on how to create electricity:

    Link to this
  2. 2. Gatnos 8:38 pm 09/12/2012

    Let me recap the situation: Everyone wants to drive an electric car because “its better for the environment.” Now suddenly they are beginning to realize that the electricity the cars use come from the local power station and charging the vehicles is causing a power crunch. Well, guess how that electricity is generated. If you are living in the US, almost 70% of the electricity production is from burning fossil fuels – yes that’s right, those evil, polluting fuels that’s causing the poles to melt, making polar bears homeless. Now compare that to France. The lucky, fresh air freaks in France get 78.1% of their electricity from Nuclear power and 11.1% from Hydroelectric. Accordingly, the perfect solution to this problem is for everyone with electric vehicles to move to France. That would alleviate the energy crunch in the US considerably. As a bonus, we wouldn’t have to listen to the electric car people whine about the lack of recharging stations anymore.

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  3. 3. jafrates 9:06 pm 09/12/2012

    @Gatnos: No one here is whining. What’s happening is a realization early on that there is a partially unanticipated consequence of electric vehicles. It’s still early, there are relatively few electric vehicles on the road, and there’s time to figure out the best way to handle it. I especially like Owl905′s suggestion of a two-stage charger since it evens out the charging throughout the day. There’s a minor loss of efficiency in exchange for a more manageable demand.

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  4. 4. Xopher425 11:18 pm 09/12/2012

    I am a big fan of electric/hybrid cars, but I’ve always thought that the advertisements for electric cars left out one thing: yeah, you’re not going to the gas station as much (if at all), but your electric bill will be going up. I also like the idea of the two stage charger.

    I wonder at the efficiency of converting fossil fuels to electricity in plants vs converting fossil fuels to kinetic motion – I’d assume there was more loss in efficiency fuel-to-motion. Anyone know the numbers or have an idea.

    Maybe one day we’ll finally perfect the hydrogen fuel cell and end these problems (but maybe come up with more?)

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  5. 5. rshoff 1:42 am 09/13/2012

    I’m just not sure that an all electric automobile infrastructure is the panacea that people believe it to be. That power still needs to be produced. Often by coal, which is much dirtier than oil. And it sounds like it would bring our antiquated electric grid to its knees.

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  6. 6. blindboy 4:27 am 09/13/2012

    I had my idea published in the magazine a while ago but I’ll restate it here. My suggestion was mainly about reducing congestion and improving energy efficiency but I think it would also solve this problem.
    In brief it is to design electric cars so they can be linked together to form a “train” powered by a mains supply rail running in a designated lane on major roads. The mains supply would also automatically charge the batteries so when the cars decoupled at their destination they would be fully charged for the rest of their journey. This would place the maximum load during peak hours when energy demand in the home and workplace is lower.

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  7. 7. Fanandala 4:48 am 09/13/2012

    @ xopher 45,
    an obvious but interesting question. Just a thumbsuck, and nothing researched, corrections would be welcomed, Coal fired boiler: 45% efficiency, turbine 90%, generator 95 %, grid 70% battery 40%, e – motor 85 %, Totals about 10 %
    Petrol powered cars are probably 15 to 20 % efficient. Diesel powered cars 25 to 30%.
    Of course if electric cars are charged with power that would otherwise not be used, that would change the calculation.
    Fuel cells will probably never be all that popular. Its not cheap to generate, extract, Hydrogen and to distribute it. And as long as fuel cells are dependent on Platinum group metals for catalysts they will not be really cheap either.

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  8. 8. BillR 8:31 am 09/13/2012

    Develop a wind/solar power storage unit at home that runs continuously storing the energy locally for charging the car. Add solar panels to the car along with a method to harvest the air flow around the car while driving to extend the charge.

    I think the biggest problem is that we cannot seem to stop thinking that we have to buy the energy from someone else who is generating it. We need to start thinking about energy self sufficiency instead.

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  9. 9. TTLG 10:56 am 09/13/2012

    Funny. No matter what time the low rates kick in, that is when everyone has their charger programmed to turn on. So that is the time there will be a big power surge. Clearly there would need to be staggered turn-on times, like the staggered work hours people have been talking about for decades to relieve rush hour traffic. Since this staggering is to benefit the utilities businesses instead of the public, my guess is that this one will actually be implemented.

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  10. 10. Kafpauzo 11:19 am 09/13/2012

    The power-surge problem can be solved with a slightly more sophisticated timer for battery charging. Let the timer automatically pick a randomly chosen moment in a one-hour interval.

    For example, if you set the timer to start charging at midnight, the timer automatically sees to it that charging kicks in at a randomly chosen moment anywhere between midnight and 1 am.

    Calculating random numbers is a well-known technique in computer programming, used for many different purposes. With correct randomization, the kick-in times of different cars will be very evenly spread through the entire hour. And with the cars evenly spread in this way, the power-distribution network should have no problems.

    Maybe sometimes a car owner needs a more exact timer setting. The timer should let them change another setting for the endpoint of the interval. For example, they might set the timer to start charging the battery at any time from midnight to a quarter past midnight, or at any time during the first minute after midnight. For the car owner, making this additional setting should be a small added hassle, so that people will tend to leave it at one hour when the exact time doesn’t matter to them.

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  11. 11. Kafpauzo 11:26 am 09/13/2012

    BillR, you can’t harvest the air flow around the car while driving.

    Any machinery that harvests energy from the air flow will brake the car much more than it can ever inject energy. If the air flow could be harvested, this would make the car a perpetual motion machine . Unfortunately, such machines are quite impossible.

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  12. 12. Kafpauzo 1:48 pm 09/13/2012

    The above-mentioned randomizing timer should also arrange a random delay when power returns after a power outage. That is, when the power comes back, the timer should wait for a random interval before it starts charging the battery.

    Without that, it may be impossible for the power company to turn the power back on when there are many cars plugged into the power network.

    Link to this
  13. 13. Profitsup 4:19 pm 09/13/2012

    Why not build more nuclear plants if you used them 24/7/365 at peak output the cost of electric power would be under 1 penny per KWH. [the price takes into consideration of stopping all E=Green law suits and delays for decades and approving a standard reactor]

    If a standard is used then they can be constructed in two or three years per unit. Connect them with a desalination plant to make fresh water from the sea water. Humm a win win win all the way around . . shall we start now no more C02 issue.

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  14. 14. VivaLaEvolucion 4:57 pm 09/13/2012

    I think that electric car manufacturers should make easily removable batteries (maybe about 50-100 lbs each) Cars could have several of these removable batteries accessible in the trunk or under the hood or somewhere easy to get to. Then, gas stations could be retrofitted with solar panels and/or wind turbines and keep hundreds of these batteries charging in a separate storage unit attached to the gas station. When an electric car pulls up, the batteries could be swapped out for a full one by a gas station attendant and the electric car can be on its way (sort of like how people swap out propane tanks) they could come in standard size. The batteries would be charged by solar panels or wind turbines on site at the gas station, so there would be no fossil fuels involved.

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  15. 15. walksoftly 6:00 pm 09/13/2012

    I don’t think it’s as big a problem as the article portrays. In many parts of Canada, every morning people get in there car & drive to work, when they get there they plug in their engine block heaters (typically 1500 watt). Some companies provide this free for their workers, others charge for it. If you use a public parking spot it’s included in the price.
    We don’t have brown outs every workday morning, because the vehicles are plugged in over a period of a couple of hours.
    If we all switched from gas to electric there would be no difference.

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  16. 16. jerryd 6:15 pm 09/13/2012

    What problem? The utilities say they can charge 50% of the US car fleet with present generation.

    There are so many solutions I use all the time with my EV’s including generating my own if needed.

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  17. 17. santaidm 8:03 pm 09/13/2012

    Ready-time should be the input by the owner, not the start time. The charging rate is set according to the charge level at the beginning. But the technical problems are minute details; the problem is politic, there has to be a plan of what is going to happen and when. Once that is set, generating capacity, smart grid, power rates, public charging stations, battery swaps, etc. all this can be easily organized.

    Not free but not difficult.

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  18. 18. cbsimkins 8:38 pm 09/13/2012

    The answer is with the utilities. It is possible, and currently being implemented in some places, for the utility to regulate the use of your air conditioners by controlling the outlet from the central office. Now the same thing can be done for car charging stations. In addition, the use of storage batteries at home, and local stations, will buffer the demand, so that the output to vehicle charging will be more level, by regulating the chargers. So when you stop at a garage to charge, it may rely upon backup batteries to provide the largest part of the charge, in wattage, and trickle recharge them when there is no demand. But the solution will need to be provided by the suppliers, who know how to maximize the efficiency of their systems.


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  19. 19. dlhfrmboi 3:04 am 09/14/2012

    In Israel, things have taken a slightly different path. Supply of electricity for cars is NOT provided by the main retail electric supplier but rather by a seperate company, which also provides the batteries, outlets and battery-changing stations. When your car is plugged into a charging outlet, the rate of energy supply to the battery is controlled by the supplier, so there’s no problem of overloading the grid. During peak demand periods, if your battery is not too low, the company may actually draw energy *out of* your battery to sell to the “regular” electric co. (There is a way to override this if you want/need to get the battery topped up as soon as possible.) And the best part is that you don’t pay for the electricty as such; you pay based on how far you drive, without regard to when you charged or changed the battery.

    There are a couple of downsides. (1) If you have an off-grid power source, e.g. solar panels, you can’t use it to charge up the car. This means there is no way to cut out the middle man or the tax man. (2) Nobody knows how to make a plug-in hybrid work with this system, so they are pretty much illegal.

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  20. 20. maxvenus 8:08 am 09/14/2012

    One thing I have never seen addressed is how road use taxes would be collected.

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  21. 21. Biodiversivist 7:32 pm 09/16/2012

    I own a Leaf. All electric cars come with a timer. Mine is set to come on at 1:00 AM and stop at an 80% charge. This is a non-issue. Utilities could easily give electric car owners an incentive to set their timers in a manner that would minimize impact.

    And yes, with today’s mix of fossil fuel power plants, an electric car is, on average, about as efficient as a Prius, the most efficient car on the road. You may as well start getting electric cars on the road now to take advantage of future low carbon energy sources.

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  22. 22. FuSci 8:36 pm 09/17/2012

    Why not put frition-based chargers by the wheels so with each turn of the wheels the batteries get some charge? It probably wouldn’t charge the whole car but it would last a lot longer….maybe. What the heck, what do I know?

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  23. 23. TweetyBird 11:49 am 09/18/2012

    The first solar powered calculator was in 1978. No one gives a second thought about using a solar powered calculator now. Can you imagine getting into your car without a thought about how to fuel the car?

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  24. 24. zzoom 4:30 am 10/15/2012

    Think about what the user wants and use technology to deliver it. People don’t want to faff about with timers and charge times and not melting the network at midnight or avoiding the echo spike at 1a.m. People want to get in the car and go at a certain time. So reverse the problem. The owner nominates when they want the car charged by, say 7am, and that’s it. The network – wifi or 3G timers or smart grid or whatever – figures out the cheapest charging profile in the available time and charges to that profile.

    Owners who allow more than minimum charging times get price reductions, as the longer the charging window the greater degrees of freedom for the timing optimisation to take place. So the price structure is a combination of how quickly you want the car charged, and times of day covered by your selected charging window. But all the user needs to do is say when they want a car charged and ready to go. The rest should be someone else’s problem.

    To me this is too obvious to not have been posted before, but from a skim I can’t see anything like it. Apologies if I missed it.

    Of course, life is complicated and plans change. With an accompanying iphone app, owners could change their charge preferences without even returning to the car, just like smart phone remote programming of your TV disk drive recorder (hands up all three electric car drivers nationwide who don’t have smart phones).

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  25. 25. zzoom 6:59 pm 10/16/2012

    Coincidentially the NBER has just posted this new paper on carbon emissions by electric car charging:


    NBER Working Paper No. 18462
    Issued in October 2012
    NBER Program(s): EEE


    Link to this
  26. 26. GreenMind 3:56 pm 11/30/2012

    I’m wondering if you could improve on blindboy’s suggestion #6. There are now stoves that heat pots using magnetic induction, and those magnetic pads that are used to charge phones by just laying them down on them. How about putting induction coils under streets and highways? At a minimum, you could put them under intersections where the cars stop, and the car could just lower a little charger to the road surface and charge up a little. It could come with a way of identifying an account to be charged for the energy, like a credit card, or maybe just be free.

    I don’t see any need for the car to be stationary though. Could you bury induction coils under the pavement in one lane of a highway? This would be better than an electric rail, due to the danger of the electricity in the rail during an accident. But an induction coil under the pavement would be a lot safer. Also, it need not be on all the time. It could turn on instantly when a car passes over it.

    Combine this with lining highways with solar panels to provide the energy during the day, and you have a nice distributed network that could propel cars with no impact on the grid at all during daylight hours, and maybe wind turbines for night.

    Link to this

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