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Tuesday, February 25, 2014

kWh > Gallons

The number of kWh that I have used for EV driving has just surpassed the number of gallons of gasoline that I have purchased in my lifetime.

Before you say it, I know these are not comparable units. Yes, they are both units that can be used to "fuel" a vehicle but they are apples and oranges. A gallon of gas will get you tens of miles. A kWh will only get you 3 or 4 miles. A gallon of gas is $3 or $4. A kWh is only about a dime. Additionally, the two vehicle types are radically different. So now that we know these are different, let's compare them anyway.

kWh Usage

I picked up my Nissan Leaf in May 2011. When I got it, I qualified for "The EV Project" program. This meant that I received a free charging station in my garage. It was installed about a week before the car arrived. When it was installed, I also installed a simple analog wattmeter (pictured below). This allowed me to count every kWh that went to the charging station.

With all the fancy features my charging station has: WiFi, timers, data collection..., the charging station's standby power is not negligible. It can add up to about 100 miles worth energy each month, so not every kWh tracked by the meter was actually used to move the car down the road, but I did pay for these to fuel the car, so they are included in this "Wall-to-wheel" analysis.

One more note, I have charged my EV in many other places. Obviously, my home meter does not track these, but home charging (typically overnight) is my primary recharging method.

Without further ado, here is my meter reading:

6060 kWh EV charging meter
6060 kilowatt-hours or 6.06 megawatt-hours used for EV fueling. I should point-out that our solar panels have made more than twice that amount since our EV first plugged in. If we had paid the standard local rate for this, it would have cost ~$600. With the Time-of-use plan that we are on, this reduced the cost to ~$388. That is not bad for 24,600 miles of driving over three years.

Gasoline usage

Calculating my gasoline usage is pretty easy since I have only ever owned one gas vehicle. A 1997 Honda Passport. When I bought it, it had 6,000 miles on it and it now it has 102,000. My lifetime MPG for this vehicle is just over 16. This means that I have purchased 5900 gallons of gas.

Computing the cost for this is not as easy. I have detailed record for 2010 and later. So for dates before this, I'll use the below chart to estimate the costs.


When I bought the Passport, I was spending less than $500 a year on gasoline. My gas costs peaked in 2008 at nearly $1500. This is when I started to drive electric. Adding the years up, I've spent over $12,000 on gasoline.

Compared


Fuel Type

Consumption

Miles

Cost

Cost per 100 miles

Electric (Leaf)
6060 kWh
24,600
    $388
  $1.58
Gasoline (Passport)
5900 gallons
96,000

$12000
$12.50

So how much have I saved over these last three years? Assuming I would have driven the Passport for these 24,600 miles, I would have used more than 1500 gallons of fuel. At a price of $3.50 per gallon, that is $5,381. Subtract the electricity cost and I have saved about $5000.