Tag Archives: electric car

EPA numbers — Nissan Leaf 99 miles per gallon?

When something appears too good to be true, I become suspicious.  When the government is providing the information…

I have been trying to figure out whether an electric car is as good as the 99 miles per gallon numbers make it sound.   I thought it would be easy.  I was WRONG.

Let’s begin by looking at data on the 2012 Nissan Leaf.   The EPA says the Leaf averages 99 miles per gallon and will use $561 worth of fuel per  year when driven 15,000 miles.

Edmunds.com says fuel will cost $1,781.  One is triple the other.   Same car, same miles per year, same MPG.  Whhaaaat?

Who’s right?   The EPA says the leaf uses 34 kilowatt hours to go 100 miles and it will cost $561 to drive 15,000 miles.  If you do the math the EPA is assuming electricity will cost 11 cents per kilowatt hour.

The EIA estimated average residential electricity rate for November 2012 for all customers  in the USA was 11.74 cents per kilowatt hour. So far the EPA looks a bit high but not too bad.

Rates vary with location.  The EIA says Hawaii is the highest at $.3672 and  Louisiana is lowest at $.0838.  The East Coast of the USA (New England + the Atlantic states) averages about $.15.

I just looked at Hawaii’s rates and the EIA estimate is wrong.  They put Hawaii a full 5 cents per kilowatt lower than Hawaiian Electric rate sheets.  The EIA is also ignoring the $9 per month charge Hawaiian Electric adds to the bill.  Hawaiian Electric has rates that encourage conservation.  As you use more your rates go even higher.  The Energy Information Administration appears to be omitting some costs… and it starts out higher than the EPA does.

If you pay less than 11 cents per kilowatt hour and you have a home charger paid for by someone else, then the EPA data might be right for you…if their efficiency data includes charging losses and vehicle efficiency is not impacted significantly by vehicle accessories.

EPA numbers have been found to be suspect in the past because the automakers perform the tests.  Both Hyundai and Ford have been recently chastised for inflated mileage numbers. Changed assumptions about vehicle efficiency and/or battery efficiency could dramatically change results.

Let’s look at the average data for the East coast.  Electricity gets to the meter for 15 cents per kilowatt hour.   It then loses about 20% of the energy going through the battery charge and discharge cycle.  I suppose the EPA might be taking that into consideration, but I doubt it.  By the time it gets to the car it costs 18 cents.

But it is necessary to install a charging system to charge the car.  Coulomb has a charging system on sale for $2789+ installation.   I’d guess you can get one installed and ready to go for $3500 to $4000.

Let’s assume it lasts long enough to allow you to drive a car 150,000 miles. $3700/150,000 miles equals 2.47 cents per mile driven.  The EPA estimates the leaf will go 2.94 miles per kilowatt hour so 2.94* 2.47 equals the cost per kilowatt hour the charging adds or 7.2 cents per kilowatt hour.  We have just assumed that the charger will last 10 years and require no maintenance…..

Now lets add everything up for the Eastern USA (New England + the Atlantic States).  We begin at $.15 for the cost of electricity, add 3 cents for the charging system inefficiency and add 7.2 cents to pay for the charger kit at the house. the total is 25.2 cents per kilowatt hour.

Now we must make an assumption on the cost of gasoline.   Let’s assume gasoline costs $3.70 per gallon.  If we pay 25.2 cents per kilowatt hour, how many miles would we have to go to spend $3.70 on fuel?

The EPA says the Leaf will use  2.94 miles per kilowatt.  At 25.2 cents per kilowatt that equals 25.2/2.94 or  8.57 cents per mile or 3.7/.0857 or 43.1 miles per gallon equivalent.

A person in New England paying $.15 for a kilowatt of electricity at his house will be able to drive 43 miles on what would be the equivalent cost for gasoline at $3.70 per gallon.   That doesn’t sound as good as 99 mpg sounds does it?

I have assumed all electricity will be provided by a home charger.  Public chargers will probably be more expensive.  I wonder what happens when it’s really hot out and the AC is on all the way.  Depending on what assumptions you make…Edmunds.com could be right.