In an attempt to satisfy government and consumer demand for better fuel efficiency and cleaner emissions, automakers are scurrying to add electric vehicle (EV) and plug-in hybrid electric vehicle (PHEV) offerings in their lineups. As these cars start showing up in virtually every vehicle class, it's likely that some consumers will start looking at electric car charging costs as they consider their next vehicle purchase.

For many U.S. consumers, the issues aren't complex: There are about 3,000 separate electric utility companies in the country and most of them offer only flat-rate billing.

When that's the case, a prospective owner of a plug-in vehicle has only to deal with selecting and installing a home charging station. Many plug-in hybrids don't even need a special charging setup. Their battery packs are small enough to be handily recharged in a few hours from a standard 120-volt wall plug.

But car buyers and owners living in urban areas often are served by utilities that have tiered pricing. The more juice consumers use each month, the more each successive kilowatt costs. Some of those utility companies offer discount rate plans for owners of vehicles with rechargeable battery packs.

In Search of the Cheapest Charge

Finding the cheapest charge for your plug-in car isn't like shopping around for cheap gas. You're stuck with the utility that serves your home or workplace and the rates it charges. But if there is a choice of plan, knowing which to pick can mean hundreds of dollars a year in electricity bill savings. Yes, electricity is cheap (particularly compared to gasoline), but the right plan in some areas can mean the difference between paying 10 cents and paying 35 cents per kilowatt-hour (kWh) of electricity. That's enough to run the typical EV for 3 or 4 miles.

It would be nice to have a listing of cities or utilities with special plans to see if your community offers you a break, but no such list exists. That's a frustration of many, including many plug-in car drivers and even the national independent Electric Power Research Institute.

Understanding the complexities of a single large utility's tiered billing structure is a herculean undertaking. Trying to digest and accurately summarize 3,000 or more plans is more than any human has so far been willing to undertake. The closest thing to a comprehensive listing that we could find is the incentives-finder tool on the GoElectricDrive Web site. Once you enter your ZIP code in the appropriate box, the tool will list most financial and non-financial incentives available to you.

In the case of electric utilities, however, it doesn't specify what special rate plans or other incentives are available. It merely identifies local utilities that have plug-in vehicle plans and provides the relevant contact information.

Call the Utility First

If you are considering a plug-in vehicle — or already have one — the best way to find out whether your electric provider has any special rate plans is simply to make a phone call.

The utilities that have EV and PHEV rates usually have trained personnel on hand to explain them. Some, like Southern California Edison (SCE), will even do a custom rate review showing you how you'd fare under each of its two EV billing programs versus sticking with the giant utility's regular five-tiered monthly household billing system.

Amazingly, a sizable number of plug-in car owners haven't made that call, according to most of the utilities in areas where plug-in vehicles have achieved a measurable degree of market penetration. A recent California-wide survey of plug-in vehicle drivers by the California Center for Sustainable Energy found that about a third of that state's owners of plug-in vehicles aren't using the electricity rate plan that could save them the most money.

Do the Charging Math Before You Buy

About half of SCE's customers with plug-in vehicles haven't bothered to call to inquire about rate plans, says Bob Graham, manager of the utility's plug-in vehicle readiness program.

"We assume they just buy the car, then go home and plug in," Graham says. "And that makes sense for a lot of them because many have PHEVs, which are easily rechargeable using standard 120-volt outlets."

Most plug-in hybrids have relatively small batteries of 8 kilowatt-hours or less. They can be recharged overnight on a 120-volt line (also called Level 1 charging).

Consumers typically understand the significant cost savings they can realize by moving from the pump to the plug. But once the decision to switch to electricity has been made, it's important for consumers to do the math relative to their unique situations.

It really doesn't matter to the utility whether you are charging at 120 volts or on a faster 240-volt charging station (also known as Level 2 charging). The cost of power is the same at whichever level you choose to charge, and recharging the car's battery will draw the same amount of power at either level.

The difference is often in the time of day the vehicle is hooked up to the charging apparatus. And that's critical when you're trying to minimize electricity costs. Many special EV charging rate plans offer reduced rates during off-peak or nighttime hours, but costs can rise dramatically if the car is still charging when the off-peak period ends.

A Brief Aside on Electric Car Charging

You could write a small book about chargers and charging, but here's the short version, as well as some terminology.

Counter to common vernacular, the "charger" is actually a component inside the car. The apparatus that hangs on the garage wall or is housed in the parking lot "charging" station is merely the communications portal and electrical supply.

Onboard chargers dictate how rapidly the battery pack can be recharged from the 240-volt Level 2 stations. Depending on the vehicle, 120-volt Level 1 charging typically delivers only about 1 to 1.5 kilowatts of power per hour, so fully recharging larger batteries on 120 volts can be a painfully lengthy process. A fully depleted 24 kWh battery pack in a Nissan Leaf takes about 21 hours to recharge using a regular 120-volt household line.

But the 3.3-kilowatt charger that's standard on the 2011 and 2012 Nissan Leaf takes on up to 3.3 kWh of electricity each hour when using 240-volt charging. That means a Leaf's fully depleted 24 kWh battery pack would need about seven hours to "fill up." A 2012 Ford Focus EV, which comes standard with a 6.6-kilowatt charger and a 23 kWh battery pack, would need only 3.5 hours on a 240-volt home charger with the proper 40-amp service. By contrast, it would take nearly 20 hours at 120 volts.

To compare all-electric range, charging times and estimated annual electricity costs at the national average of 12 cents per kilowatt, check out the side-by-side comparison tool on the federal Energy Department's Web site. Click on the "Advanced Vehicles and Fuels" tab to get links for both full EVs and plug-in hybrids.

Picking an EV Charging Plan

Graham said that about half of the plug-in owners or shoppers who call SCE to see how to minimize their electric bills pick the utility's whole-house time-of-use plan. It lets them charge the car between midnight and 6 a.m. for rates as low as 10 cents per kWh. The utility also believes that whatever plan they pick, most of its customers who have plug-in vehicles do the majority of their charging at night, which is good for the grid.

One cautionary note: An EV owner using the slower 120-volt charging during an off-peak period should make sure that charging is completed during the period. Otherwise, the cost of a full charge will include some peak-period rates and might be more than a 240-volt user would pay.

Time-of-use plans typically divide the day into various "peak," "mid-peak" and "off-peak" blocks, charging more for power that's used when demand is high and less for low-demand periods. Off-peak blocks are typically very late at night, such as SCE's midnight to 6 a.m. bargain-charging period. Mid-peak periods are typically early morning and late evening hours.

Some utilities, including SCE, also offer separate meter service for plug-in vehicle owners. The home charger is wired directly from a separately metered line and the cost for power to the charger is billed at a lower rate than the consumer's regular household power.

One problem with separately metered plans, though, is that the cost of installing that separate meter can be prohibitive, eating up any savings the lower EV charging bill might bring during the time you own the car.

Timing Matters

Plug-in buyers with home solar systems or electricity conservation habits that keep them in their utility's lowest pricing tiers may be better off sticking with the regular household plan. That's because switching to a time-of-use plan often results in hefty peak-period charges aimed at discouraging daytime power use and reducing the peak-period load on the grid.

A plug-in owner who doesn't have solar power and who works at home or has heavy daytime use of air-conditioning and such appliances as electric clothes dryers also could be better off sticking with a "normal" plan, rather than facing the higher peak-period rates in a time-of-use plan, says Don Anair, a senior engineer with the Union of Concerned Scientists' Clean Vehicles Program.

Savings Will Vary

Anair recently took a stab at analyzing special EV rate plans from major urban utilities and found that such plans exist in at least 14 states. His benchmark was $100 a year in savings versus the utilities' standard household plans.

The plug-in car charging rate comparison on page 25 of the Union of Concerned Scientists' recent "State of Charge" report assumed that the EV or PHEV was driven 30 miles a day at an efficiency level of 3 miles per kWh and was recharged at 240 volts.

The biggest savings were in California, where electricity rates are among the highest in the nation.

Topping the list was the separately metered EV time-of-use plan offered by Pacific Gas and Electric Co., which serves the San Francisco and Silicon Valley region. Owners there could realize savings from $1,006 to $1,068 a year by switching from PG&E's standard rates to the EV time-of-use rate.

The biggest savings outside California were for New York City customers of Con Edison: $342 a year using either a whole-house time-of-use plan or a separately metered EV time-of-use plan.

At the bottom of the list, Boston-area customers of NSTAR Electric could save $100 a year using either the utility's whole-house time-of-use plan or its separately metered time-of-use plan.

As cars with plugs become more common, utilities, automakers and electric-drive proponents are likely to get their acts together and make charging rate information a lot easier to find.

Meanwhile, the best advice is to call your local utility and ask for help in figuring out the best plan for your circumstances. And remember that just as with fuel efficiency, your savings may vary.