# Nissan Leaf MPG Numbers Very Flawed

Cross-posted from Coyote Blog

The EPA has done the fuel economy rating for the all-electric Nissan Leaf.  I see two major problems with it, but first, here is the window sticker, from this article

Problem #1:  Greenhouse gas estimate is a total crock.  Zero?

The Greenhouse gas rating, in the bottom right corner, is that the car produces ZERO greenhouse gasses.  While I suppose this is technically true, it is wildly misleading.  In almost every case, the production of the electricity to charge the car does create greenhouse gasses.  One might argue the answer is zero in the Pacific Northwest where most power is hydro, but even in heavy hydro/nuclear areas, the incremental marginal demand is typically picked up by natural gas turbines.  And in the Midwest, the Leaf will basically be coal powered, and studies have shown it to create potentially more CO2 than burning gasoline.  I understand that this metric is hard, because it depends on where you are and even what time of day you charge the car, but the EPA in all this complexity chose to use the one number – zero – that is least likely to be the correct answer.

Problems #2:  Apples and oranges comparison of electricity and gasoline.

To understand the problem, look at the methodology:

So, how does the EPA calculate mpg for an electric car? Nissan’s presser says the EPA uses a formula where 33.7 kWhs are equivalent to one gallon of gasoline energy

To get 33.7 kWhs to one gallon, they have basically done a conversion through BTUs — ie 1 KWh = 3412 BTU and one gallon of gasoline releases 115,000 BTU of energy in combustion.

Am I the only one that sees the problem?  They are comparing apples and oranges.  The gasoline number is a potential energy number — which given inefficiencies (not to mention the second law of thermodynamics) we can never fully capture as useful work out of the fuel.  They are measuring the potential energy in the gasoline before we start to try to convert it to a useful form.  However, with electricity, they are measuring the energy after we have already done much of this conversion and suffered most of the losses.

They are therefore giving the electric vehicle a huge break.  When we measure mpg on a traditional car, the efficiency takes a hit due to conversion efficiencies and heat losses in combustion.  The same thing happens when we generate electricity, but the electric car in this measurement is not being saddled with these losses while the traditional car does have to bear these costs.  Measuring how efficient the Leaf is at using electricity from an electric outlet is roughly equivalent to measuring how efficient my car is at using the energy in the drive shaft.

An apples to apples comparison would compare the traditional car’s MPG with the Leaf’s miles per gallon of gasoline (or gasoline equivalent) that would have to be burned to generate the electricity it uses.  Even if a power plant were operating at 50% efficiency (which I think is actually high and ignores transmission losses) this reduces the Leaf’s MPG down to 50, which is good but in line with several very efficient traditional cars.

## 35 thoughts on “Nissan Leaf MPG Numbers Very Flawed”

1. Richard A. says:

True, but I would think a counter argument would be that it’s a lot easier to muzzle the CO2 from a relatively few plants than from a whole lot more individual cars. Plus whatever method is used to generate electricity happens to come around, all cars automatically switch to that source technically speaking, which means future costs of conversion to new fuel sources would be limited to switching the grid as opposed to having to find a gasoline substitute.

All assuming the technology advances and eventually you could drive these thing a good bit further. 100 miles doesn’t even cover my daily commute. And I’m disappointed, I would have liked to have had one of these things just for the cool gadget factor.

2. Brego says:

The sticker also reveals that the car will only last 1 hour and 13 minutes on a full charge and then go completely dead. Grandma is going to have to move closer to town if she expects a visit on Xmas.

3. Juggling the figures a bit, the 73 mile range gives 25kwh of charge in the battery – about 5 pints of gasoline. In terms of pure efficiency the electric carwins hands down. A coal or diesel-engined powered station can be over 90% efficient, compared with 25% for a gasoline-powered car (and up to 38% for a diesel engine truck with constant load. There are some transmission and conversion losses to consider. But practically it is far better to have the power station within the car than have a portable energy store. Economically, considering the very limited supply of some chemcials within these batteries, there can only be a relatively small number of affordable electric cars.

4. Juggling the figures a bit, the 73 mile range gives 25kwh of charge in the battery – about 5 pints of gasoline. In terms of pure efficiency the electric carwins hands down. A coal or diesel-engined powered station can be over 90% efficient, compared with 25% for a gasoline-powered car (and up to 38% for a diesel engine truck with constant load. There are some transmission and conversion losses to consider. But practically it is far better to have the power station within the car than have a portable energy store. Economically, considering the very limited supply of some chemcials within these batteries, there can only be a relatively small number of affordable electric cars.

5. Juggling the figures a bit, the 73 mile range gives 25kwh of charge in the battery – about 5 pints of gasoline. In terms of pure efficiency the electric carwins hands down. A coal or diesel-engined powered station can be over 90% efficient, compared with 25% for a gasoline-powered car (and up to 38% for a diesel engine truck with constant load. There are some transmission and conversion losses to consider. But practically it is far better to have the power station within the car than have a portable energy store. Economically, considering the very limited supply of some chemcials within these batteries, there can only be a relatively small number of affordable electric cars.

6. LoneSnark says:

you are wrong. Power stations get pretty darn efficient, but no where near 90% unless they are recapturing the waste for heating nearby neighborhoods, but most stations don’t do that.

7. Luis Dias says:

this reduces the Leaf’s MPG down to 50, which is good but in line with several very efficient traditional cars.

What cars achieve anything near 30%, let alone 50%? I’m completely unaware of these magical devices…

8. I wrote an article in my blog at http://hamiltonianfunction.blogspot.com/2010/02/nissan-leaf.html regarding the leaf. The conclusion is that aerodynamically and rolling resistance wise, it’s good but not exceptional. It would be an unusual situation where the gasoline burned by an internal combustion engine in an otherwise equivalent car would emit less carbon than even the coal burned to generate the electricity used to motivate the Leaf over the same distance. Not impossible but rare.

9. Well, at the end of the day, we’ll never have a car that produces ZERO greenhouse gasses. Even a solar powered car would need solar panels and a storage device, whose manufacture would contribute to greenhouse gasses. The reduction, though, is significant.

10. Russ R. says:

I agree with “Problem #1”. Yes, the zero GHG rating entirely ignores the GHGs emitted in the production of the electricity. It’s not incorrect to say the CAR ITSELF emits no GHGs, but it’s more than a bit misleading to pay no attention to the GHGs behind the curtain.

However, I don’t agree with “Problem #2” as it’s presented. Maybe converting kWh and gallons of gasoline to BTUs isn’t the best way to frame an MPG equivalence, but your idea of trying to calculate the amount of gasoline that would be burned to produce the electricity is impossibly complex given the wide variety of power generation systems that feed into the grid, and the substantial daily change in the generation mix from base load hours to peak load hours.

The better option would be to not report an “MPG Equivalent”, and simply show buyers the vehicle’s miles per kWh rating. They can do the math themselves, comparing the price per kWh they pay to their utility company vs. the price per gallon they would pay at the pump.

My simple price-based math: At the time of writing this, US retail gasoline prices average \$2.85 per gallon, and US retail electricity prices average \$0.12 cents per kWh. Buyers can use their own local prices.

The 34 kWh required to drive 100 miles would cost \$0.12 x 34 = \$4.08.
At \$2.85 per gallon, that \$4.08 would purchase 1.43 gallons of gasoline. 100 miles on 1.43 gallons equals 69.85 MPG, which is very good, but materially lower than the 99 MPG that the EPA reports.

11. cracovian says:

#1 made sense to me initially but energy used to produce and distribute gasoline/diesel is not taken into consideration when establishing MPG numbers for conventional cars. So stating that the car itself doesn’t emit greenhouse gases is technically correct – you’d now penalize the electrics if you looked at what’s being used and emitted to produce electricity to power the cars unless you’d do the same for everyone (and don’t forget those ridiculous, energy-hogging, and subsidized ethanol mixes.)

#2 to me as a consumer and in terms of the actual costs (I’m getting my LEAF in April) is somewhere in between those numbers (~75 MPG) if I compare the cost of electricity vs. current gas prices. I suspect it will only get better as gas outpaces electricity prices.

Either way, it’s tricky stuff but we haven’t seen nothing yet – I wonder what they will do with the Volt where GM was claiming 200+ MPG –talk about ridiculous and a hybrid that doesn’t really seem to be that much more efficient than a Prius in the city and the mileage getting down to ~33 MPG during extended trips.

12. Wally says:

I certainly agree on all general points, and I think other posters have threshed out any issues I have with them.

However, the real problems posed by these cars is simple practicality. This car might be great for moving around in short distances with limited numbers of people and stuff, but longer commutes and family activities are out. No one is going to want to recharge their car 4 or 5 times going from say LA to PHX. (How long do those charges take anyway? I’m guessing they can’t beat a 3 minute fill up.) Nor for hauling Becky, Kim and Jimmy to and from their various types of football games.

This is why Americans buy fairly large cars. We simply like to do stuff and don’t want to, or can’t, buy a second or third car just for daily commuting.

So if the Leaf fits your needs, great. Buy one. I’m sure it will be an excellent car for the job. But this car fills a very small niche in the American automobile market. And until the technology is able to push the equivalent of a Chevy Tahoe 300 miles or more, from a population-wide stand point, it will be little more than a gimmick.

13. cracovian says:

Wally – There’s no need to rehash it to death. For the majority of people this will be a second, third, etc. car in the family. I know I’m keeping my Sienna for long hauls (more room for all the kids and safer on top of that) and the SUV for utility and towing. But even as a third car, it will cover 50-60% of our mileage needs (daily school drop offs, shopping, weekend trips to the zoo.) Only 20K are made for us in the first year, so you can bet there will be enough demand to consider it one the hottest car on the market for a while. Even with 1 in 100 families wanting one, Nissan will have an upper hand for many years to come.

14. FDUK says:

Russ, it may be only equivalent to 69mpg in the US, but here in England it woudl be equivalebnt to 120 mpg because the cost of fuel is so much higher (~£5.15 pg, so the cost of fuel will be critical to any calculation, and that varies.

15. barryjo says:

Why are we still yammering about GHG emissions??? If that red herring were removed, would this “car” (vehicle) still make sense? Also, the rare earths needed to make them are basically controlled by China. This could become a very limiting factor in their manufacture.
As a cute toy they may(?) make sense but in practical terms, all they do is clutter up the already crowded highways and byways.

16. jorgekafkazar says:

Well, we’re being fed a line of BS, that’s for sure. When will all the lies come to an end?

Typically calculations only extend to operational characteristics. End-to-end the numbers are very different. The recent offerings are pretty awful.

I think it’s time for a full-sized V8 truck.

18. Dave says:

This is great news! This means I can buy a Corvette Z06 (with a 500 HP engine that gets 19 MPG) and a Nissan Leaf, and my fleet average will still be 59 MPG! I thought it would be impossible for us to achieve a US fleet average of 42 MPG for cars by 2016, but this makes it possible. I should’ve known our government would lie their way out of this dilemma. Of course the sticker is dishonest, but nobody cares about accurate science anymore. The problem I see is the \$561 per year electricity cost. If they don’t start building new power plants soon, coal or nuclear, this figure will quickly double or triple, along with the cost to heat and cool our houses!

19. Wally says:

Cracovian,

I’d love to see the poll and the poll questions/methods that says 1/100 families want a Leaf.

Sure in the abstract it would be great to just have that car sitting around. But how many families really want to spend the roughly \$25K to buy one and then the maybe \$100/month to insure it? What if they actually had pay the full price? (Which brings up a larger issue, that if this technology where to expand to a significant chunk of the market, our nation couldn’t afford the 7.5K handout per car)

Maybe it works for you, as a upper middle class family that can afford one (with the handout) who also has a long commute, but for most people this car will be completely impractical. So, its nice that it works for you, and you can thank me, and everyone here, for subsidizing your commute cost. But this technology is not even close to being truly competitive with conventional cars. And what ever market advantage you think Nessan is capturing, it is completely fabricated and could disappear at almost any moment.

20. Ktaylor says:

The EV’s charging would be at night, when most generators in powerplants are running and putting out little. It seems people wish to beat up the emmission levels and continue to justify driving ancient pieces of junk, paying for maintenance, paying more for GAS and never seeing past anything but negative behavior, rather then seeing the benefits of the EV. Getting away from OIL. The EV having far less moving parts and higher reliability. Very low manitenance. Longer life the the ICE and its drivetrain. The cost reduction with increased production and sales as with all new technologies. The list goes on. Electric devices are far more efficient then fuel powered devices. As an Electronics technician, I se little reason for not owning an electric car. Don’t be scammed by people who write negative articles. Your welcome to your GAS HOGS. Their replacement with new technologies is long overdue.

Wally,

The correct way to read the 1/100 poll is that 1% of the families would actually keep (and perhaps even occasionally drive) a Leaf, if it was given to them free of charge (no pun intended).

Personally I’d think anything 99/100 folks didn’t want even for free meets the description “couldn’t give it away” pretty well.

22. robler says:

A friend of mine who knows batteries well says owners will only be able to recharge the car batteries around 500 times. Then they will need a new battery. Also that battery technology is already well-developed; there will be only limited technological/efficiency improvement in them; and they will cost \$10,000 or more to replace.

If he is right, the cars are horrendously more expensive than the auto manufacturers or government are letting on. What do you all think?

23. mbabbitt says:

Just give me an Audi TDI diesel. Enough said.

24. Wally says:

Ktaylor,

Fewer moving parts? Yeah, ok, if we don’t count electrons, I guess. Which brings up the maintance cost of replacing those batteries. And how much do you really want to think about disposal of all these batteries, particularly, if electric vehicals come to make up a significant chunk of the car market? Which then brings up another point: What happens to your lax night time power grid if we have millions of cars being charged every night?

The Leaf is cute, and maybe a decent step towards an improvement in personal transportation, but its just not there. Not by a long shot.

25. I like the range of comments on here. I think RussR is giving the most reflective and even-handed response.

#1 – The estimate is for the car, not for the total energy cost. All fuel types should have their source costs analyzed.
#2 – I like the idea of claiming the Miles per KWh. It has to be a apples to oranges comparison though; electricity vs petrol.

Batteries – It seems some folks are still in the dark about battery tech. Some very high percentage of batteries, like 99%, are recycled. It is true that older Lithium Ion batteries could only be recharged around 500 times, but very cool improvements are coming, like the SCiB battery by Toshiba which can charge to 90% in 5 minutes. Nissan is providing an 8 year warranty on the battery. They also have a version that costs about \$1k more which comes with a 480V charging station and can charge to 80% in ~30 mins.

Quite a large percentage of people in the US live in cities (like 81%). The national average for miles driven per person per day in the US is ~35. Based on these numbers, I could see this car as quite a good buy for quite a few people.

The real obstacle, as demonstrated by the comments here and the author, is the paradigm shift in the consumer’s perception of their own travel needs and their attitude towards electric cars. They are still pretty new and the concept is unnerving to many… but they are gaining traction. Electric cars have been around for decades. That they are being discussed by news media and are going to be for sale (not just custom built) is huge.

26. robler says:

Dross, it seems to me the electric car can only serve as a utility vehicle. Virtually everyone who owns one will need a second car as well: the range on the e-cars is too small.

Did you notice that Chevy has changed the range numbers for the Volt, to 25 to 50? i.e. it may not even cover that average miles driven figure you cited. And an average is just that: an average. Some days people will drive little or no miles. But then when they do drive, they must go further distances than the average indicates.

I’m not clear about my recharging question. Are you saying the future batteries might hold more than 500 charges? If so, how many? And is this theoretical, or are the batteries already showing doing this?

A 500 charge battery must be replaced every 12,500 to 25,000 miles. At current costs, that means you must spend another \$10,000+ every two years or so. This is probably why some car manufacturers are leasing the batteries, I believe at around \$100 or so a month.

Wally (the post directly above yours) asks some good questions about disposing the batteries, and also what impact on the power grid (and cost) millions of electric cars charging each night would have. Do you have any reactions to that?

Thanks…

27. Wally says:

Dross,

The recycling of Li batteries isn’t exactly cheap, easy or even particularly “green.” You shouldn’t confuse recycling something, with a lack of waste. You’re often just exchanging one waste for another. For example the Li-batteries need to be cooled to -325 F. It takes a lot of energy to do that. Plus, we still need to get the infrastructure in place to transport and store the batteries, not to mention to actually handle recycling the volume of batteries that would be created with millions of electric vehicles running around. I’d like to see the total energy/CO2 equation, because it sure isn’t clear to me, when everything is considered, electric vehicles are even close to competitive.

I’ve also heard about that ~30 minute charge to 80%, but that still doesn’t do you much good if you’re trying to drive more than 70-100 miles in a stretch. So you drive for an hour, maybe hour and half, and then you wait for 30 minutes…. Now my 12 hour drive to see family is 16-18 hours? Its just not practical. Even with most people not driving like that often, the lack of flexibility is a big knock, and leads to the requirement of a second or third car. Which in the global “green” equation, the shear fact that you have to build that extra car, the process of which consumes about as much energy as a car will use for transportation in its lifetime, makes it a much better idea to just not have the specialty commuter car in the first place.

28. Wally says:

mbabbitt,

It would sure be nice if we could by the Audi A4 TDI… Another thing to thank California for.

29. Waste your money however your want, but just don’t expect me to fund your foolishness with tax credits and what not!

30. BillBoy says:

In an interview on the BBC yesterday, as the government announced a subsidy on 8 different electric cars, it was claimed that if all car/truck etc journeys in America were done using electric vehicles then the US would have to up its total electricity output by 34 times. That is alot of coal powered stations to be built. I cant claim this is true or where it was taken from but if this is true or even close it shows that electric cars are not really a sustainable way forward.

31. bobuk says:

Brego: said,

The sticker also reveals that the car will only last 1 hour and 13 minutes on a full charge and then go completely dead. Grandma is going to have to move closer to town if she expects a visit on Xmas.
November 23, 2010, 2:37 pm

Does the quoted rang include, lights on, heater or air con on, radio on, electric windows, sat nav on.

32. robler says:

Following up on bobuk’s comment, does the range include climbing hills? The frequent acceleration needed in city driving (from lights, stop signs, reacting to traffic, etc.)?

I also wonder how many people will really get the full range out of each charge. To do so they must schedule their driving so the charge runs out just as they reach either their home or a recharging station. (For now, most likely their home.) Would seem very hard to do.

A comparison would be trying to time the gasoline in your car so it goes empty just as you pull into the gas station. Cutting it too close. In fact, I think most people don’t wait till there are only 25 to 50 miles left in their tank to gas up. They would be too nervous to drive around with such little mileage left.

33. robler says:

It won’t surprise me if many people mostly drive the Volt as a gasoline car. The electric range is so small, and it takes so much time to charge. Gasoline will prove far more convenient for most driving, IMO.

34. Chris Calcroft says:

We rarely drive without the car heater being on. A care has plenty of low grade (waste)heat but in an electric car de-misting or heating can seriously reduce the range and hence the efficiency. Stuck in a traffic jam in cold weather would be a nightmare.

Also, at the moment electricity is barely taxed yet petrol (gasoline) has taxes on taxes on taxes. Here in the UK petrol tax is enormous, so imagine what the UK goverment would do if petrol cars were replaced by electric!