The real costs for electric cars

What if a gallon of gasoline cost $2 in the middle of the night, was free at lunch and set you back $8 in the afternoon? Welcome to the world of electric cars. If you buy one, the cost of a fill-up will largely depend on when and where you recharge it, not to mention the rates your utility company offers.

In the U.S., the cost of electricity varies far more widely than the cost of gasoline, from a kilowatt-hour average of 8 cents in Washington state to 36 cents in Hawaii (a kilowatt-hour (kWh) is the amount of electrical energy consumed when 1,000 watts are used for one hour). Someday soon, you might be able to recharge your electric vehicle (EV) for free during a lunch stop at the mall. But if the EV is going to be filled up at home, your rate could be much higher than the national average of 11 cents that the EPA will put on its fuel economy label for EVs.

Because of the variety of utility rates in the U.S., a 2011 Nissan Leaf that's a bargain to drive in Washington — $28.29 for 1,000 miles — is pricey in Hawaii, where those 1,000 miles would cost $97.21. A conventional car getting 36 mpg would make that trip for the same money. For consumers primarily interested in driving an EV to save money, it's critical to know actual electric rates (and the current cost of gasoline, for comparison purposes) instead of relying on national averages.

To figure out the cost of fueling an EV, start with the electric car's energy consumption rate, which is expressed as kWh per 100 miles (kWh/100m). This figure will be listed on the EPA's upcoming EV fuel economy label (the 2011 Leaf's preliminary label is shown here, complete with an erroneous 12-cent per kWh figure in the cost estimate that Nissan says it is correcting). The next figure is your home electric rate, assuming that's the primary charging site. Multiply the kWh/100m figure by the electric rate to get the cost per 100 miles. For instance, the Leaf's kWh/100m figure is 34. If electricity is 11 cents per kWh — the national average — it would cost $3.74 to go 100 miles.

Another way to calculate cost is to use the number of kilowatt-hours it takes to recharge the EV's battery. If an EV requires 20 kWh to fully recharge, and the rate is 11 cents per kWh, that's $2.20 to fill up the car. What does that equal in mpg? See that equation discussed here. Rather than worry about mpg, cost-conscious EV buyers should focus on how to get car-charging kWh at the lowest rates.

Rate Schedules
The cost of electricity is based on the rates set by utility companies, time of use and level of use. The more electricity you use, the more you pay for it. And consumers generally pay more per kWh for electricity used at peak hours. Unless EV buyers do some planning, they could find themselves paying rates much higher than the national average of 11 cents per kWh.

In California, for example, Southern California Edison (SCE) has five rate tiers for residential users, largely based on usage, and they range from 12 cents per kWh to 31 cents. The cost of electric-vehicle charging could easily fall into the most expensive tier, since the electric car is being added to a household's existing demands for powering such things as heating, cooling, lighting and entertainment systems.

SCE is offering EV owners two plans to avoid kWh sticker shock, says Edward Kjaer, director of plug-in-vehicle readiness at SCE. One uses a tiered structure that's similar to the utility's standard residential rate, but provides a "super off-peak" rate of 10 cents per kWh from midnight to 6 a.m., which is when many EV owners will charge up. The peak rate during the day, which is when SCE is supplying power to its business customers, is 55 cents per kWh.

SCE's other plan is a time-of-use rate. To take advantage of it, consumers must pay to have a second meter installed that only measures electricity used to charge the EV. They'll then be billed at a separate rate from the rest of the home. The rates for this plan are discounted to 11 cents per kWh for charging that occurs off-peak — before noon and after 9 p.m. SCE says the time-of-use option can give customers the lowest rates for EV charging, but it also involves more initial setup cost and time.

Kjaer suggests consumers who are serious about buying EVs should contact their local utility companies as early in the shopping process as possible to get guidance in choosing the rate that's best for them. SCE has resources that are specific to its customers, but there's also good general information there on EV readiness.

Real-World Experience
New Jersey restaurant owner Tom Moloughney has been driving an all-electric Mini E for 17 months and 45,000 miles. He's fanatical about logging data about his driving experiences and writes about them on his own blog.

Moloughney's Mini E has an energy consumption rate of 38 kWh per 100 miles — less efficient than the Leaf's 34 kWh/100m. But the Mini E also has 201 horsepower versus the Leaf's 107. Moloughney can choose between two electricity rates: 18 cents per kWh at home and a commercial rate of 12 cents at his restaurant in Montclair, New Jersey, where he installed an additional 220-volt charger.

"I charge at work as much as possible," Moloughney said. "It's the difference between paying $3.20 for a full charge at work — which is about 100 miles — and $5.25 at home for that same full battery."

With gasoline prices in the $3 per gallon range in New Jersey, driving an EV is saving Moloughney money. He'd have to get 66 mpg in a conventional vehicle to match his workplace cost of charging the Mini E. But the Mini E would be less economical if he just relied on his home charging rate of 18 cents per kWh. Then it's comparable to a conventional car getting 44 mpg.

Tom and Cathy Saxton, computer programmers who live in Sammamish, Washington, are a two-EV family: They have a 2002 Toyota RAV4 EV and a 2008 Tesla Roadster. They installed separate electric meters for the EVs in July 2009 and have been tracking energy use since then. The Saxton's Tesla is consuming at a rate of 30.8 kWh/100m (bettering its official EPA rating); the RAV4 is averaging about 35 kWh/100m.

The Saxtons pay 11.25 cents per kWh. But rather than describing their energy costs in terms of kWh per 100 miles, Saxton said he and his wife tell friends that their vehicles travel about 30 miles on a dollar's worth of electricity. Of course, that is a dollar's worth at 11.25 cents per kWh. If they were in Hawaii, where electricity is nearly 30 cents per kWh, it would be a much more expensive drive.

As the EPA mileage sticker for the Nissan Leaf reminds us, your results may vary, depending not only on the efficiency of the EV you're driving but also where and when you're charging it. The true cost of filling up your electric car turns out to be far more complicated than anyone expected.