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Published on October 9th, 2011 | by Breath on the Wind


Electric Vehicle: Cost of Electricity

October 9th, 2011 by  

There is a growing interest in electric vehicles (EVs), with many vehicles now being offered and planned for future release. The uninspired and those who may be in the employ of the Koch Machine will long and loudly rail against the EV for its status as a ZEV. But, at ground level, especially in difficult economic times. it is the vehicle’s cost that will motivate mass adoption of electric cars.

There are a number of ways to determine EV costs. Where we don’t have accurate information. we must generalize or make assumptions. Long-term maintenance, resale value, and even insurance rates may change as we get more experience with electric vehicles. We can determine a carbon footprint, but this also requires some generalizations. And a higher purchase price has to be balanced against lower operating costs. What we can calculate with good accuracy is the cost in electricity per month.

The electrical cost of an EV is determined by

1. The cost of your local electric rates. Your home bill is the best place to find this information, but the DOE EIA produces lists of averages by state. At $0.3458 per kWh, electricity will cost you about the most in Hawaii, while, at $0.0809, it is about the cheapest in Idaho.

2. Modifications to the normal rate.
— Your electric bill will probably have a minimum payment amount. If you don’t use the minimum amount you will be paying for it anyway.
Time of use rating — in most places you can get deep discounts by using a special meter that is smart enough to tell when you are using the electricity at off peak hours. The electric rate may be 1/2 or less the daytime rate.
Net metering: solar panels — If you have solar PV panels on your roof you may also be on net metering. The total cost of electricity will then be the difference between what you sell to the utility (typically at peak daytime rates) and your usage. When combined with an EV charging at off-peak rates at night, the combination of solar PV panels and an electric car is very attractive. There are now even online calculators to help you decide how many solar panels you would need.

3. How much you drive the vehicle. If you don’t drive the car, you are not using fuel. The average mileage for each driver is an estimate that varies depending upon what source you consult. In the US, this ranges from about 12,000 to 15,000 for the average driver in a year. The Federal Highway Administration shows that totals vary by age and gender, but it also varies substantially based on whether you live in an urban or rural area. While the EPA uses 15,000 miles, its overall average is 13,467 miles per driver. This amounts to (13476/12 =) 1,123 miles per month. A useful figure for an EV driver is likely less, as it is unlikely that an electric car would presently be used in rural settings where we expect longer driving distances.

4. What vehicle. The economy of a vehicle will be affected by many factors, including wind resistance, (including frontal area) rolling resistance, drivetrain efficiency, and the weight of the vehicle. Smaller, lighter, aerodynamic vehicles with special tires (or rails) will be more efficient and cheaper to operate. A vehicle with bigger or smaller batteries will change the range for the vehicle but not the operating costs.

Is a smaller battery better? It will charge faster, but do you care if you are sleeping at the time. We don’t fret about the time because it is similar to the time it takes to wash our clothes. We can be at home and doing other things and not focusing our attention being in a line or fueling a vehicle. If you are afraid you might forget to plug it in, you could use a wireless charger.

Evatran's Plugless Power wireless/proximity charging system

We have a lot of information about the Nissan Leaf. The EPA vehicle mileage is 73 miles on a full charge. This would imply a complete charge (1123 monthly miles/73miles/charge) about 15.38 times a month or about every second day (or 1/2 a full charge every day.) It has a 24 kWh battery capacity. We can assume a charger efficiency of about 95%, so that the total electrical usage to charge the battery from empty will be around (24/.95=) 25.26 kWh. Using this range and battery capacity (25.26KW-hr/73 miles = ) gives us .346 kWh/mile. This is similar to the gas mileage in a petrol vehicle.

For comparison, a 3-ton air conditioner (36,000 BTU) is the size that might be used to cool a small house or a storefront. Typical spec say that it will draw 20 amps at 230 volts or (230 x 20 =) 4600 watts in one hour (4.6 kWh.) In about 5 and a half hours (25.26/4.6) of continuous operation it will equal the power demands of a Nissan Leaf full charge. (The charge time for the Leaf is longer, as the supplied power is not constant to better condition the battery.) The AC only works this way to initially cool a hot building. In normal usage, it is maintaining a temperature and cycling on and off.

The monthly mileage is then used to derive the monthly kWhs (1123 miles x .346 kWh/mile =) 388.56 kWh / month and in

Hawaii the vehicle might cost ($ .3458 x 388.56 kWh = ) $134.36/month ($1612.32/yr) while in

Idaho it might cost ($ .0809 x 388.56 kWh =) $31.43/month ($377.16/yr). Both of these numbers are without any of the modifications mentioned above. For additional savings, use special metering and/or solar panels.

No matter where you live, the price is likely to be about 1/2 to 1/4 of what you would pay for gasoline.

About accuracy: Any calculations are only as good as the assumptions and information available. We can quickly find an error in calculations, but the reasons for using those numbers are sometimes harder to find. There are many variables here and it is a good project for a spreadsheet analysis. There are also online calculators that will make some of the assumptions for you.

Feel free to give us your location (state) and actual costs in the comments section.

Photo Credits:
EV charger: OregonDOT
Car plug: futureatlas.com
Lithium ion battery: NASA
parking lot solar panels: USFWS mountain-prairie
Evatran wireless charger: Evatran via Autoblog Green

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About the Author

We share this World; its past, present resources and our combined future. With every aspiration, the very molecules we use for life are passed to others through time and space so that each of us may be considered a Breath on the Wind. This part of the world's consciousness lives in NYC; has worked in law, research, construction, engineering; has traveled, often drawn to Asia; writes on Energy and Electric Vehicle issues and looks forward to all your comments.   "If you would persuade, you must appeal to interest rather than intellect." -- Benjamin Franklin

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  • Rob Barchard

    A large portion of the cost of gas here in Alberta goes is collected as tax and is intended to be spent toward road maintenance and other related costs. I am curious to see that if / when electric vehicles become more standardized, if electricity rates will be adjusted to reflect capture lost revenues? Will electric car owners use separate meters for their vehicles, or would the cost be spread around all electric vehicle users?
    Another interesting thing about electric vehicles is their environmental impact. It’s important to consider the where and how electricity is produced. ex- burning coal to make steal to turn turbines to turn generators which produce electricity which gets transformed to high voltage to be transmitted long distances to be transformed to low voltages, to charge a battery to turn an electric motor has a very low net efficiency, and potentially significantly higher carbon dioxide emissions than burning gasoline.

    • Bob_Wallace

      How EVs will be assessed for road use is an undetermined question. It probably would be reasonable to charge a fee based on miles driven per year.

      If there was a 100% coal-fed grid then EVs might mean slightly more CO2 production than an efficient gasmobile. There are at least two studies which find “slightly”, not “significantly”. Don’t overlook the incredible ineffecency of an internal combustion engine. Roughly 20% of the energy in a gallon of gas gets turned into vehicle motion.

      Furthermore, I think you’ll have to look long and hard to find a 100% coal-fed grid.

      Last year the US grid was 42% coal and so far this year coal is contributing 39%. Coal is on its way out.

      I think you get about 45% of your electricity in Alberta.

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  • Breath on the Wind

    Thanks for coming along with such experience and thoughtful records. I have tried unsuccessfully to obtain the number you provided: The actual available battery capacity. This will be reduced over time and like a larger or smaller battery should not make any difference to the operating cost of the vehicle.

    Where it will make a difference is if the ratio between full charge and the full charge range changes. You don’t give any indication of what kind of mileage you are able to get from full charge to full charge. This is a lot like gas mileage. If your driving technique is actually more conservative and closer to hypermiling techniques you will get better mileage. Someone else might not do as well.

    You have actual numbers but I am trying to make some general predictions that may help others to do the same. Each has value. If we had 100 people giving a similar history as yours we could begin to make some general predictions. For now your data is certainly good for you and it certainly may be good for others. We simply need more of this kind of information.

    As you pointed out there are several assumptions in your pages. Several stick out for me:

    You expect electric prices to rise in some equal percentage to oil prices. This has not historically happened and unless you live in Hawaii there is no reason it should. Less than 1% of the US energy mix uses oil to produce electricity.

    For any particular driver, their driving history is the same no matter what vehicle they are driving. Insurance rates are unlikely to make any difference in comparing a petrol to electric vehicle.

    You don’t give your vehicle any residual value after 7-9 years. I am very hard on vehicles and like you this may be true for me. A brother however will keep a vehicle for 20 years and have it look like it just came from the factory. Some commercial experience with electric buses compared to petrol buses suggest that electrics last about 8 TIMES LONGER! I don’t know if we will see electric vehicles with residual values higher than petrol vehicles but we may. If technology vastly improves and can’t be retrofitted then we may have a situation like computer technology.

    But I think it is more likely that someone would rather get their hands on an old electric vehicle for modifications than a petrol vehicle that they might then convert to electric. Those people will always find electrics more valuable. If oil prices rise and electrics continue to be in short supply. Used electric vehicles could be valued even higher than new ones.

    I am preparing another article on battery and vehicle costs. I hope you will come back to that as well. Thanks again.

    • Anonymous

      Just a couple of points…

      Places such as Texas and Spain which have installed a lot of wind generation have enjoyed a decrease in electricity prices. That should hold for other locations as well. Wind generation is improving and prices will drop.

      New transmission is being built to bring Wyoming’s wind to the West Coast. That will likely drop electricity prices in that area.

      Solar (large roof arrays in sunny locations) is now about $0.15/kWh. This is less than the cost of gas peakers and the price of solar is expected to continue its rapid drop.

      It’s fairly likely that electricity prices will stay stable or drop over time.

      Hawaii is starting to move from oil generation to renewables. Electricity prices will drop there.

      There apparently is data that shows that more fuel efficient (cheaper to operate) vehicles command higher resale prices. That should certainly be true for EVs. Even a Leaf whose range might have dropped from 100 miles to 80 miles after several years is going to be very attractive to someone who can live with the lower range. With a ten year old, 100,000 mile-driven ICEV one would be expecting mechanical costs to rise. That shouldn’t be the case with EVs.

      I don’t know how accurate they are, but I’ve seen reports of Leaf drivers using only 0.25kWh/mile. Seems like they are coming out of the LA area so warm weather and perhaps not many hills. I would imagine that these drivers are trying to produce low numbers. That said, the feedback systems built into EVs might encourage many drivers to conserve.

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