Rating the Leaf & Volt

The EPA has determined that the Nissan Leaf gets 99 mpg, which is really interesting since the Leaf doesn't have a gas engine. 

The EPA has also determined that the Chevy Volt gets 93 mpg in all electric mode.  The stickers for both cars are included below. 

You could argue that the mpg rating for an electric vehicle must be either zero or infinite, but a better comparison would be miles per dollar or dollars per mile. So let's compare the Volt and Leaf with a gas powered car.

Here's the math for a dollars and cents comparison:

Nissan Leaf - 34 kWh per 100 miles or 4,080 kWh for 12,000 miles. At $0.16 per kWh that works out to $653 a year or $0.0544 / mile. 

Chevy Volt - 36 kWh per 100 miles (all electric) or 4,320 for 12,000 miles. That works out to $691 a year or $0.0576 / mile. 

If you assume half your miles are powered by plugging in and half from filling up - the numbers work out like this. 

6000 miles / 37 mpg = 162 gallons x $3 a gallon = $486 for gas + $345 for electricity = $832 a year or $0.0693 / mile.

A 24 mpg gas car would use 500 gallons a year at $3 a gallon which equals $1,500 a year or $0.125 / mile. 

That's 2.3x the cost per mile of a Leaf and 1.8x the cost per mile of a Volt.  

So a Leaf will save you $847 a year and the Volt will save you $668 a year in operating expenses. 

Here's the math for CO2 emissions. 

The EPA sticker also claims that the Nissan Leaf produces 0 pounds of CO2 which will be true for those of us who get their electricity from renewable sources like rooftop solar panels or NSTAR Green. 

Here's the math if you get your conventionally generated electricity from NSTAR. 

Conventional electricity in Massachusetts generates 1.28 pounds of CO2 emissions per kWh. 

Gasoline generates 19.56 pounds of CO2 emissions per gallon. 

A conventional electricity powered Nissan Leaf will generate 4,080 kWh x 1.28 pounds of CO2 per kWh = 5,222 pounds of CO2. 

A Chevy Volt will generate 2,160 kWh x 1.28 pounds of CO2 per kWh + 162 gallons x 19.56 pounds of CO2 per gallon = 5,933 pounds of CO2. 

A gas powered car will generate 500 gallons x 19.56 pounds per gallon = 9,780 pounds of CO2  or 1.87 times more than a Leaf or 1.65 times more than a Volt. 

If you read the fine print you may be surprised to learn that the EPA assumes that Nissan Leaf will be paying $0.12 per kWh, but that the Chevy Volt will be paying $0.11 per kWh. It's been a long time since anyone in Lexington paid 11 or 12 cents a kWh for their electricity.