## December 27, 2010

### Chevy Volt Efficiency

Little over two years ago I wrote an article asking Will a Chevy Volt be a good buy?    I concluded then that a Volt would not save me a ton and that a Prius would be a better buy financially.

I only had preliminary information on the Volt when I wrote that first article.  Now that the Volt is actually a real car theres more concrete information.   An article Hyped hybrid: The Chevy Volt gets average mileage, for a hybrid via Yahoo from Consumer Reports looked at the fuel efficiency of the Chevy Volt.

This is the meat of the article as far as I'm concerned:
"Over numerous trips, our collective average for electric-only range was 33 miles. Once the battery is depleted and the car is essentially using only gasoline as its fuel, we averaged 30 mpg overall in mixed driving"

Electric fuel cost
They got 33 miles off a battery charge and charging the battery takes 12.5 kWh of electricity.  At 10¢ per kWh thats \$1.25 cost in electricity to drive about 33 miles.   So each mile costs about 3.8¢    If gasoline costs \$2.75 then thats equivalent to a car that gets 72 MPG as far as fuel cost/mile.

Gasoline fuel cost
When the Volt is running on gasoline they saw fuel efficiency of 30MPG average and thats a easy comparison to standard gasoline cars.

The purely electric fuel cost is great.   The gasoline fuel efficiency of a Volt is OK but nothing special.

Hows it compare to a Prius?

I'm going to assume electricity costs 10¢ per gallon and that gasoline costs \$2.75.  If electricity is cheaper then that favors a Volt but if its more expensive that puts the Volt at a disadvantage.   The more expensive gasoline is then the more it costs to drive a Prius and the better the Volt favors.

Lets say you drive 30 miles a day every day of the year.   That would be pure electric driving.   You'd be driving nearly 11k miles a year and your cost would be about \$456 per year.  If you drove 11k miles a year in a Prius at 50MPG and gas costs \$2.75 then you'd be paying \$605 in gasoline.   So you're saving about \$211 a year in fuel on the first 30 miles per day of driving with a Volt over a Prius.  However after the first 30 miles a day you'd be getting only 30MPG with the Volt compared to 50 MPG with a Prius.

Lets say you average 40 miles a day.   Your electric cost for the Volt is still \$456 but now you've got another 10 miles a day or 3650 miles a year driven on gasoline.  The gasoline miles are 30 MPG so you're buying about 121 gallons of gas.  At \$2.75 a gallon that would cost \$333 roughly.   SO 40 miles a day on a Volt is about \$789.   40 miles a day on a Prius is 14,600 miles.   With 50MPG that would be 292 gallons of gasoline.  The cost of \$2.75 per gallon means total cost of \$803.   If you drive 40 miles a day then the Volt saves you only about \$15 a year over a Prius.

Lets look at 50 miles a day.   The Volt drives 30 miles on electricity for a cost of \$456.  It drives 20 miles on gasoline for a cost of \$669.   Total cost for 50 miles a day over a year would be \$1125.  The Prius gets 50 MPG so you're looking at \$2.75 a day if driving 50 miles a day.   Thats an annual cost of \$1003.   Now if you're driving 50 miles a day on average the Prius is \$120 cheaper than the Volt.

Here's the summary of annual fuel costs:

 miles/day Volt Prius 30 \$456 \$605 40 \$789 \$803 50 \$1,125 \$1,003

Again this assumes arbitrary fixed electric cost of 11¢ per kWh and gas at \$2.75 per gallon.

The more you drive the more a Prius beats a Volt.

Now of course we should keep in mind that people don't drive the same exact amount every day of the year.  Your driving will vary from day to day.   You might drive 30 miles round trip to work Monday through Friday and then drive another 25 miles on Tuesday to go out to dinner, 10 miles on Saturday to go to the store and and 40 miles on Sunday to go to church then visit a friend.   Then 2 times a year you might take a 500 mile road trip to visit family out of state.

I'm assuming the Consumer Reports data is valid and accurate.

Bottom Line : Based on Consumer Reports findings it really appears to me that a Volt is not more efficient financially than a Prius.   My original verdict is reinforced:  A Prius is a better buy than a Volt.