Case Studies

Disclaimer: rambling stream of consciousness follows:

I drive an EV with a 244 mile range, if I was driving more than 200 miles in a day I would probably average recharging after going 150 miles whenever I was near a place that was convenient to stop.
Assume I have time of use billing available to pay for my electricity. 5.5cents per kWhr at night, and 21 cents per kWhr during the day. ( see previous entry for details on this ) How much will I spend on electricity vs gas for different use scenarios?
Note that a 30 mile per gallon car would cost you 10 cents per mile at 3 dollars a gallon.

My round trip to work is 28 miles. Lets round it up to 30 miles.
Multiply by 5 days * 50 weeks = 7500 miles per year.
On the weekends I could imagine driving another 150 miles split between saturday and sunday ( or spread over a couple of trips during the week ). Thats another 7500 miles, for a total of 15000.
If that was my driving pattern, 100% of my charging would happen at night, when we have surplus power and I should be able to buy power for about 5.5cents pew kWhr.
About 3000 kWhr of energy for 165 dollars or 1.1 cents per mile.
A 30 mpg gas car would use $1500 of gas.

Suppose that 10 weekends a year I drove 800 miles ( 400 miles per day ) instead of the 150. Or 20 days during the week I drive 400 miles instead of my usual 30 mile roundtrip. ( Remember 400 miles in a day is 7 hours on the road )
Now we are at 21500 or 22400 miles per year ( lets average to 22000 ). I would need to charge 250 miles of range each day during the day, at peak prices. The other 150 miles worth would be charged overnight. So now I am charging 5000 miles worth of range during peak, contributing to the max load of the day.
77% of my charging still happens at night, and 23% during the day.
I use about 4400 kWhr and pay $154 + $336 = $490 or 2.2 cents per mile.
A 30 mpg gas car would use $2200 worth of gas.

Suppose I have some kind of job where I drive around a lot. I work 7 days a week and every day I average 200 miles. Thats 70,000 miles per year. Suppose that the mileage varies and some days I only drive 100 miles and some days 300 miles. On the 200 mile days, I know they are going to be 200 mile days and charge at home every night. Lets say 10% of the days are 100 mile days and 10% are 300 mile days. Thats 36 days a year at 300 miles, and on those 36 days I charge 150 miles worth during the day at peak times. Thats 5400 miles of charging during peak times or about 8%. The other 92% of my charging happens overnight.
My electricity costs me $711 + 227$ = $938 or 1.3 cents per mile.
A 30mpg gas car would use $7000 worth of gas.

Lets redo the last scenario but always stupidly charge to full after 150 miles in the middle of the day. So all of those 200 mile days you end up charging 150 during the day and only 50 at night.
Electricity cost would be $250 + $1985 = $2235 or 3.2 cents per mile.
Once again the 30mpg gas car would use $7000 worth of gas.

Obviously all the scenarios above 20000 miles a year are very unlikely. The average american actually drives 12000 miles per year. The more you drive, the more you save by not burning gas, but even if you drive ridiculous distances every day a 200+ mile range electric car works way better than a gas car.


One response to “Case Studies

  1. Andrew Bienhaus

    Has anyone with your car, done much to add solar panels for times parked in sunny areas?

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