Nissan Leaf EPA rating of "99mpg" is, sadly, a lie.


Nissan is touting that the EPA gave the new Leaf a mileage rating of 99mpg "gasoline equivalent". What is not said in some stories (though Nissan admits it in the press release) is that this is based on the EPA rating a gallon of gasoline as equivalent to 33.7 kwh, and the EPA judging that the car only goes 73 miles on its 24kwh battery.

There is a huge problem with these numbers. If it were possible to convert perfectly, a gallon of gasoline actually has about 36kwh, so possibly the EPA is factoring in the 7% loss of electrical distribution. But in reality it isn't even remotely possible to convert fuel to electricity perfectly.

I have written and update on comparing gasoline and electricity with more details.

The Department of Energy, for example, offers a number which puts under 13kwh as the energy equivalent of a gallon of gasoline. That's how many kwh you get out of the plug if you burn coal, gas or oil with roughly the same energy as that gallon of gas. With the DoE's number, the Leaf is getting a combined mileage of around 36 mpg-equivalent. That's not a bad number, but there are many gasoline cars that do better than that. Even a Lexus hybrid does similar to that. This is no minor error, it's a massive one, and it's highly unlikely that Nissan or the EPA are unaware of it. This gives the impression of an attempt to make the Leaf seem way, way better than it is to promote electric cars. The problem with that is that when people learn the truth, they are going to be unhappy, and will be soured on electric cars, Nissan and the EPA.

Now I will agree that there is justifiable debate over the right way to do this calculation. The DoE works from its calculation of the average efficiency of power plants in the USA. People in areas with more efficient power will do better using electricity than those close to old coal plants (which are the big drag-down here.) The DoE also counts BTUs in nuclear plants (which provide about 20% of U.S. energy) as BTUs even though no fossil fuel is burned and no greenhouse gas is emitted. People must judge for themselves how "dirty" they think nuclear BTUs are, and how to value an electric car in areas where most of the electricity is nuclear. Even harder to judge are the 10% of US kwh that come from hydro. Hydro doesn't even have BTUs or pollution, though it does come with environmental destruction. If you live in the Pacific Northwest or parts of Canada where most of the power is from hydro, you may judge the 99mpg number as more realistic, though in this case the concept of a gasoline equivalent is stretched pretty thin.

If you live in California, which burns almost no coal and gets most of its power from natural gas, and then nuclear, the real number isn't as bad as the national average, but it's still nowhere close to 99mpg. If you live in a place that is almost all-coal, like Utah or New Mexico, electric cars are not so great an idea -- their only environmental advantage is that the fuel source is domestic rather than imported, and the coal is burned elsewhere, not right next to you.

There are other electric cars that are more efficient than the Leaf, but the big reality is that to really beat out the 50mph gasoline hybrids you need to make your car lighter.

"But wait," some people say. We can run our electric car on solar or renewables and all is wonderful! Don't get me started on this. There are no solar electrons. Installing renewable generation can be a good idea, but you must tie it to the grid for it to work. Not tying solar or wind or other sources to the grid is highly wasteful, because the power is discarded any time the battery is not empty (or worse, not connected.) Grid tie makes the grid greener, and people who do that can feel good about it if they do it well, but it does't make driving more than a tiny smidgen of a percent greener than it was.

Shame on Nissan and the EPA. I hope that at least, Nissan will only sell the car in places with electricity that is well above average in quality, and refuse to sell it in places where the power is mostly from coal.

Not that I don't understand the motivation. Had the EPA rated the car with the DoE methodology number of 36mpg, it might well have killed the car at the starting gate. It's an interesting moral question if it's right to lie to kickstart a technology which will become better with time. They could also have lobbied for a more reasonable but generous mpg, perhaps derived from the best natural gas plants, which would have offered a number in the 50s. Not nearly as exciting but not a car-killer, though the comparison to the Prius or Insight would not look so good.

It would have been best if they had just developed a new standard, like watt-hours/mile or miles/kwh, and leave it to the press and local power utilities to publish local conversions between "kwh" and gallons. (Not the dealers, they can't be trusted of course.) It actually would be quite handy if every power utility were to publish, for each zone the local efficiency of the power grid in terms of BTU/kwh or greenhouse effect/kwh.

Update on Chevy Volt: The numbers for the Volt were released. As a plug-in Hybrid that can go 35 miles on its batteries and then has a gasoline engine, they rated it as 97mpg while on the battery (similar false number to the Leaf) and 37mpg while on gasoline. These numbers are actually roughly the same when using electricity at the grid national average.

Sad to say, but if you live in a place where the power comes from coal, the math seems to say you should remove most of the batteries and save the weight.


How about looking at it this way: 0.15$ Cost per Kwh X 24 = 3.60$ per fill up (that takes me 77 miles). That means that it costs ~ 5 cents per mile. To do the same with a car when gas costs ~3.00$ per gallon would mean you would have to get ~60 miles per gallon.
Now of course the cost of gas and electricity will vary but it is easy to convert into cost per mile.

There is a lot of variation in the price of electricity, and it even varies based on the time of day. In California, high electricity users pay a fortune (like 30 cents/kwh) but there are exemptions from that for people who have an electric car. The real global price of gasoline is more like $8/gallon but it's kept low in the USA.

I have planned to write a post about the cost per mile of the electric car, and how to figure out what the battery costs per mile, as the battery is (in a different way) a consumable. Of course, so is the engine and drive train of a gasoline car.

We're still trying to figure out just how long these batteries are going to last, though, and what they will be worth when done. However, most calculations show the battery as costing more per mile than the electricity.

Also worth noting: the cost of electricity is kept low because of the cost of coal and natural gas.

I don't know what you're pontificating about Brad, but here's the truth, as I see it behind the steering wheel of Sparkey, my Leaf.

MY greatest fear is running out of electrons. It's called "Range Anxiety". I have a 60 mile R/T commute. Consequently, I drive like very conservatively. It's called "Hypermiling". I'm not very good at it, but I regularly achieve 5 miles per KWh.

Where I live I'm on a voluntary electric pricing plan that is cheaper during off peak hours. I can charge my Leaf between 1 AM-5 AM for 5 cents/KWh. (I'm asleep, BTW, the car charges then automatically.:-) The math isn't hard. It works out to a penny a mile. SO, what's gas costing YOU right now? $3.50 a gallon? $4.00? More?

Well, at $4 a gallon, my Leaf goes the equivalent of FOUR HUNDRED MILES per GALLON!!! That makes a Hybrid touring 50 mpg look pretty sad...

Don't dis my Leaf, man...

200 wh/mile is very good for the Leaf. Nissan doesn't rate it that highly but it does sound possible with hypermiling. However, most people can't get 5 cents/kwh but it's nice that you can.

However, the big question in electric cars is the battery lifetime. The battery cost dwarfs the cost of the electricity. The Leaf's pack is estimated to cost $18,000. If you get 150K miles out of it -- this is hard to judge but the car itself is not likely to get more than 200K, then the battery pack is costing 12 cents/mile. So it doesn't matter a lot if the electricity is 1 cent/mile, 2 cents/mile or even free.

The truth is, that depending on your full battery useful lifetime, the reality of an electric car is you are buying all your fuel up front when you buy the car, and pay a tiny amount extra for the actual electricity. This can still beat the cost of gasoline of course, though not by a lot.

It seems kind of useless to put an MPG rating on the vehicle that doesn't use the "G" part. Are they doing this to fulfill some kind of Federal regulation? Or is it just a marketing gimmick?

But it's clear that if you're going to pitch a car as a green choice -- and far fewer would buy the Leaf if they did not think it was a green choice -- then you have to help people compare to their gasoline car. Had the EPA said, "OK, we will call that 37mpg" then Nissan and others would have lobbied like hell to either change that or have the EPA do what would make more sense, namely watt-hours/mile or miles/kwh. But for whatever reason, they got the EPA to do what paints their car in the most positive light possible, a number based on near-perfect conversion of fuel to electricity.

Now I know there are reasons to buy an electric car other than to be green. They are silent, novel, have some cool features, are cheap to operate on a cost/mile basis that doesn't include the cost of the car and should be easier to maintain. All good things but unfortunately offset by range anxiety.

If MPG starts at the pump, MPGe should start at the plug.

Yes, electricity comes from dirty sources, but it's unfair to saddle the mpg-equivalent number with the energy costs of generating and distributing the electricity to EVs when the mpg number for gasoline cars isn't similarly saddled with the energy costs of militarily defending access to oil, drilling the oil, shipping it across the ocean, refining it, loading it into trucks to distribute to gas stations, and the energy costs of operating those gas stations (I'm sure I missed some energy costs in there).

MPG and MPGe are used because the public has a general feel for them, but they must be used EITHER as measures of efficiency, OR as measures of environmental impact - not both.
If you want it to be a measure of efficiency, go with the 99 mpge number.
If you want it to be a measure of environmental impact, go with the 36 mpge number, BUT then revise down the mpg numbers of gasoline-powered cars to make the comparison meaningful.

The latter option is much more fuzzy, open-ended, and politically charged, so I'd say lets stick with the former.

But your comment suggests the answer you want, which is to look at the total life cycle cost of both. That is definitely not what you get by the very misleading use of mpg at the pump and mpge at the plug.

Most of the cost of the oil has been well studied, and the general number I see is that 81-82% of well energy makes it to the pump or tank. I've seen less on the cost of mining, processing and shipping of coal to power plants. The cost of the military is much harder to put into the equation so we usually don't see it.

If it's efficiency you want, then you want to compare the power at the DOE number of 10,300 BTUs per KWH, modified by what we can learn about the extraction cost of the fuels, and you want to use the well cost of gasoline, which as noted is 22% higher than the pump cost.

If it's GHG you want, I believe the number above is a reasonable estimate.

In terms of total life cycle cost of EVs-on-coal, Tesla Motors used to have some very thorough white papers available on their website, but alas, no longer. All that's left is this, which you may still find interesting:
From what I remember though, the total per/mile energy cost of driving a Tesla Roadster charged on electricity generated from a the average American dirty-coal power plant was still much less than the per/mile energy cost of a Prius (it should be noted that the Leaf isn't as energy-efficient as the Roadster, at 34kWh/100mi vs. the Roadster's 27.1 kWh/100mi)

I don't like the idea of using life-cycle costs, however, because the factors that are hard to quantify are still very real. Our energy and pollution challenges are complex ones, and the use of MPG and MPGe invites the consumer to switch off their brain and assume all the thinking has been done for them already (it hasn't). For gasoline-powered cars, the cost of oil wars is very real, and should be considered. For EVs, the benefit of moving the pollution of millions of cars upstream to a single energy source (which can be replaced with a cleaner energy source) is very real, and should be considered.

I agree that MPGe's of any kind are misleading in different ways, and I hope they quickly give way to Wh/mi. While they're still with us, the only truly objective measure is what the vehicle can do with the energy it's supplied with, regardless of the production cost of that energy, leading to that 99 MPGe figure. As a writer with an audience, if you call that figure a lie (as is your right) and make the discussion about life cycle costs, you should in the same breath
- mention that MPG figures are a lie as well, and adjust them by 20%
- discuss all the not-so-easily-quantifiable costs, pro's, and con's of BOTH energy sources.

There are of course different places to measure the energy from. The most complete is well (or mine) to wheels, but that is harder to get numbers on. Fuel to wheels is what the DoE uses and that gives a ready source of numbers that have been researched and that's why I have often used this. The coal, natural gas and even uranium took energy to get out of the ground and get to the power plant, though probably not as much as the gasoline.

All the numbers that aren't full life cycle will mislead a bit, but the use of plug to wheels is just too far off the mark. From an energy standpoint, it's an error of 3x, and that just can't be accepted while an error of 20% is much more tolerable. Even from the GHG standpoint it can be an error of anywhere from on the chart from less than 1x all the way to 3x.

So has anybody added the cost of the oil wars? I believe the Iraq war cost was around $750B, spread over several years. Spread that over 15 years -- though it's hard to say just how many years of oil such a war bought -- that's about 1.5 trillion gallons of gasoline, or an extra cost in the range of 50 cents/gallon. Your mileage may vary, but that's actually less than I would have guessed. Not that I'm saying we want to justify wars over gasoline based on the cost per gallon!

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