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.

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