Published on October 9th, 2011 | by Breath on the Wind9
Electric Vehicle: Cost of Electricity
October 9th, 2011 by Breath on the Wind
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.
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.
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