Is electric car fuel efficiency a fraud? Leaf gets 25 mpg?

[Piggy]

Just got a link via email entitled:

EPA Fraud: Chevy Volt, Nissan Leaf Actually Get Only 23, 25 MPG

The blog post's subhead says:

The MPG figure must be calculated where the energy is produced. Doesn't matter if that happens in the car's engine ... or in the coal plant, as with the Leaf and Volt.

Here's the gist of the argument:

The current “miles per gallon equivalent” is a fraud perpetrated to hide the true environmental cost of these cars. One gallon of gas does have about 33.5 kilowatt-hours of chemical potential (depending on blend, additives, etc). And about that much energy is needed to get the Leaf to go 99 miles, and the Volt to go 93. But here’s where the fraud is perpetrated: the electricity for those vehicles is being generated by mostly coal power plants that are only about 33% efficient (minus transmission losses and losses from charging). Coal plants are off-site power generators (whereas car engines are on-board) and are totally ignored in the EPA rating.

The blogger gives a hypothetical a little later:

Let’s say you took your gas-guzzling engine out of your car and hooked it up to a generator in your garage. The engine has a fuel efficiency of 15 MPG. That’s roughly 25% efficient (a 300 HP engine burns about 1000 HP of gas). You run the engine to generate electricity (let’s assume, just for kicks, that the generator hooked up to your car engine is 100% efficient) to charge your Nissan Leaf or Chevy Volt. Guess what the mileage of that Leaf is? The EPA says you will still get 99 MPG overall. But you actually used four gallons, not one, to get that far, thanks to the charging engine’s 25% efficiency.

The real efficiency of the Leaf is dependent on the efficiency of the coal power plant: the Leaf gets 25 MPG, not 99. The Chevy Volt gets 23 MPG, not 93.

Now, I'm not averse to the notion that someone (EPA or auto companies) may be playing fast and loose here. But I also notice that no mention is made of inefficiencies at gasoline refineries. So what gives?

I don't know enough about any of this to evaluate it at all.

Can anyone with expertise in this area chime in and give a layman's explanation of whether these accusations hold water or not?

Thanks.

 

[ponderingturtle]

In a fairly direct sense it is probably best to compare $ per mile not some hypothetical gallons per mile. That will result fairly well in efficiency.

 

[Loss Leader]

It's true that the car's energy has to come from somewhere. And it's true that a depressing amount of the US energy supply comes from coal. Coal is a major contributor to acid rain, CO2, CO and other really bad byproducts.

However, gasoline engines are also sources of polution, and liberate carbon pretty much the same way coal plants do. As with everything, efficiency is easier at scale. A hundred million small engines are more difficult to correct than 100 coal plants.

As the energy burden shifts from the individual car to the plant, new technologies can make the plants cleaner, more efficient or even obsolete. A gas engine a hundred years from now is still going to burn gas. But your electric sockets don't care whether the wires are bringing in burned gas, coal, natural gas or nuclear, water or wind.

Electric cars will result in lower emissions overall.

 

[casebro]

What kind of efficiency? Cost per mile can be added up. Emmissions? The power plants are only about 5% cleaner than the latest autos.Mpg? The OP has the right idea, though I think a bit exaggerated. I would believe about 35 mpg, because that is doable by similar cars, and power plant efficiency is a bit better, or we would have internal combustion engines in our air conditioners.

So the efficiency of the hybrid or electric is not a simple slam-dunk. But the "Ecos" like the concept, for now.

 

[Dr. Trintignant]

It's safe to say that the numbers should be considered bogus until proven otherwise. Further, as casebro says, there is no mention of what kind of efficiency is meant (though given that it's from freerepublic.com, I have to assume they aren't referring to CO2). .

The Volt and Leaf appear to be wins on virtually any useful metric, but it's always possible to invent a bizarre metric on which something loses.

- Dr. Trintignant

 

[Piggy]

FWIW, wiki discussions of the Volt's Monroney label and fuel efficiency in general.

 

[Furcifer]

Just some correction, for all intents and purposes the Volt and the Leaf won't really affect baseload production of electricity. which is generally coal. Off hours generation is picked up by peakers such as co-gen plants which operate at about +60% efficiency on natural gas.

You can't really say where your electricity is coming from, but if you say it's from coal I say it's from nuclear, we can argue all day about it and neither of us is going to be correct.

If everyone plugs in their Volt of Leaf at 9PM you're really using that residual energy as the peak demand drops and plants begin to shut down and start venting steam. You're kind of using wasted electricity. At least for now.

As the number of electric cars grows the peak will flatten out and the cost per megawatt should theoretically drop as more peakers bid for off hours that they would normally be shut down anyways.

As an example, right now if you were going to generate for 4 hours you might need $150/ Mwh to even consider firing up. With more electric cars, you can fire up for 8 hours at $100/Mwh because running a turbine for 4 additional hours is cake. That has a considerable effect on your efficiency as well, obviously running continuously for 8 hours is a lot more efficient than running for 4 hours on 2 different days.

As you can see there's A LOT more to it than using coal plant efficiency to determine environmental costs of these cars. This isn't even a ball park figure. I can't determine what the environmental costs of these cars will be in the long run, but I'm fairly confident in saying the first million cars will be doing a lot of good for a lot of people because of the way electricity is currently generated.

 

[steve s]

If more businesses would do something like this we wouldn't need to rely on coal plants so much.



Steve S

 

[casebro]

FWIW, wiki discussions of the Volt's Monroney label and fuel efficiency in general.

Looks like the OP was correct, the 99 mpg figure is based on thermal output from the gasoline, rather than actual efficiency of any particular power plant. Which is also mentioned up-thread at 60%.for a natural gas plant.

 

[Piggy]

I'm afraid I'm not following this thread very well at all.

It's going to take some spoon-feeding, folks.

It seems to me that the EPA is saying, "All right, if you run your car on a charge from your socket, then -- on average in today's USA -- you can expect that if you get a charge produced by what amounts to your grid power source consuming the equivalent of one gallon of gasoline, it will go X miles on that charge... say 93".

Is that a correct thumbnail of what EPA means when it gives an e-car a 93 MPGe rating for electric-only operation?

If that's correct, then does their math hold up? Is it accurate? Is it reasonable to say that my Chevy Volt, if I drove it 93 miles on electricity only, would require a charge that could be provided from the grid by the use of resources equivalent to the consumption of 1 gallon of gas?

 

[Piggy]

Looks like the OP was correct, the 99 mpg figure is based on thermal output from the gasoline, rather than actual efficiency of any particular power plant. Which is also mentioned up-thread at 60%.for a natural gas plant.

So are you saying that EPA does its calculations on something like the assumption that my electrical socket is actually being powered by a gasoline-fueled generator?

Not that they really believe that's the case, but that this is how they do their calculations -- in other words, if I did use a gas-powered generator to run my house, and I charged my Volt with that system, it would go 93 miles on a charge that required one gallon of gas to perform?

If that's true, then how relevant is that to the reality of how my power is actually provided? Or is there simply no clear way of answering that, even on average for the US?

 

[Dr. Trintignant]

you can expect that if you get a charge produced by what amounts to your grid power source consuming the equivalent of one gallon of gasoline

What does equivalent mean? This is important because power plants don't burn gasoline. Do you mean carbon-emission-equivalent, or cost-equivalent, or something else? Does it matter if you live in France, where ~80% of electricity is from nuclear, vs., oh, West Virginia? Do you calculate based on the marginal increase in electricity use or the national average? Does it matter if the charging is done at night when there might be a different mix of generation?

The link in the OP doesn't even begin to consider these questions. The EPA has. One might quibble with their numbers but one has to look at it in detail to form a valid argument against them.

- Dr. Trintignant

 

[casebro]

No, what we are sying is that the EPA estimates uses the KWH (electricity quantity), converts it mathematically to the "thermal content" of gasoline for it's equivalency. They leave out the inefficiency of actual electrical generation.

They do NOT use the amount of gasoline that it would take to make the electricity used to power the car.

The difference between the two is large, between 40-70%, depending on the power plant and the fuel it uses. Coal plants, IIRC, waste 70% of the energy, meaning the car would only get 30 mpg if it happened to run on electricity generated from coal.

I suppose there is a variable fudge factor involved, depending on fuel, plant etc. But the 99mpg looks more like 40-50 to me.

I suppose there are enough owners now that somewhere on the web is real costs, in cents per mile, for various electricity rates.

Hmm, looks to me that new cars ought to come with those stickers from water heaters and air conditioners? "This appliance will cost $xxx per year for the average family of four."

 

[macdoc]

Piggy - forget about the miles per gallon etc.

A gasoline engine is not very efficient in it's production of useable mechanical energy from fossil fuel - it's somewhere around 3% once all factors are accounted for for converting chemical in the ground to mechanical over the ground. ( transport of fuel, refining etc etc etc. )

Even the dirtiest coal plants do better than that and then EVs are are just plain far more efficient at converting electricity to mechanical. The electrical to chemical ( grid input to battery ) has some loss as does the transmission through the grid.

Unlike other vehicles EVs can be fed from anything that supplies electrical power and they convert that power quite effectively. Solar and wind.

Following the chain of energy conversions and losses and recaptures in the chain can be very daunting and one feature is as mentioned EVs capture power that is most often off peak.

They are a good fit with a partial wind system where the power can be erratic.
The mechanical to electrical power off the wind is converted to chemical in the battery then back to electrical and then to mechanical to do useful work....drive you around.
Good EVs can recapture some of the mechanical back to electrical, then back to chemical by turning the braking system into a generator.
SuperCaps would be ideal for that as there is loss in the chemical transition and also an inability to capture the energy fast and release it fast.

Rest assured the EVs are a positive step forward in carbon reduction - so so in some areas ( coal fired grid ), brilliantly so in others. ( hydro, nuclear, wind or solar supplied areas ).

 

[Piggy]

What does equivalent mean? This is important because power plants don't burn gasoline. Do you mean carbon-emission-equivalent, or cost-equivalent, or something else? Does it matter if you live in France, where ~80% of electricity is from nuclear, vs., oh, West Virginia? Do you calculate based on the marginal increase in electricity use or the national average? Does it matter if the charging is done at night when there might be a different mix of generation?

The link in the OP doesn't even begin to consider these questions. The EPA has. One might quibble with their numbers but one has to look at it in detail to form a valid argument against them.

- Dr. Trintignant

I'm sortof looking for answers to these questions, you know. So simply posing them doesn't help me much, I'm afraid.

But I don't think carbon-emission equivalent is what the EPA is after at all. That wouldn't make any sense, as far as I can see, when you're talking about a Monroney sticker, which is not intended to measure such things.

I also don't think cost-equivalence is in the picture, either, for the same reason.

Nor do I think France matters here.

So what exactly is EPA saying their MPGe means? I suppose that's what I'm getting at.

I can see it making sense in this scenario:

Suppose I charged my e-car by using a gasoline-powered generator. If I burned one gallon of gasoline in the generator, then I could get enough of a charge on my car's battery that I could drive it for 93 miles.

That would be a clear MPGe of 93.

Of course, EPA would have no way of knowing what kind of generator any given person might use, so their math in that case might reflect some sort of average -- perhaps a mean or mode for home-use gasoline-powered generators sold in the US.

But since that's not likely to be the case for any e-car buyer, I assume this is not how EPA arrives at its Monroney figures. Although I could be wrong.

The only thing that makes sense to me is that they're making certain assumptions about the power that comes out of the socket in my garage.

So if we assume -- for no particular reason, just for this hypothetical here -- that EPA were basing their figures on power from a relatively new coal-fired plant, then yeah, that leads us right to the question you mention: What is the coal equivalent of one gallon of gasoline?

My view would be that the coal equivalent of one gallon of gasoline would be whatever mass of coal has the same potential energy, when combusted, as a gallon of gasoline.

 

[Piggy]

No, what we are sying is that the EPA estimates uses the KWH (electricity quantity), converts it mathematically to the "thermal content" of gasoline for it's equivalency. They leave out the inefficiency of actual electrical generation.

They do NOT use the amount of gasoline that it would take to make the electricity used to power the car.

The difference between the two is large, between 40-70%, depending on the power plant and the fuel it uses. Coal plants, IIRC, waste 70% of the energy, meaning the car would only get 30 mpg if it happened to run on electricity generated from coal.

I suppose there is a variable fudge factor involved, depending on fuel, plant etc. But the 99mpg looks more like 40-50 to me.

I suppose there are enough owners now that somewhere on the web is real costs, in cents per mile, for various electricity rates.

Hmm, looks to me that new cars ought to come with those stickers from water heaters and air conditioners? "This appliance will cost $xxx per year for the average family of four."

I'm sorry, but you're failing to understand the degree of simplification you're going to have to employ here.

 

[Piggy]

Piggy - forget about the miles per gallon etc.

A gasoline engine is not very efficient in it's production of useable mechanical energy from fossil fuel - it's somewhere around 3% once all factors are accounted for for converting chemical in the ground to mechanical over the ground. ( transport of fuel, refining etc etc etc. )

Even the dirtiest coal plants do better than that and then EVs are are just plain far more efficient at converting electricity to mechanical. The electrical to chemical ( grid input to battery ) has some loss as does the transmission through the grid.

Unlike other vehicles EVs can be fed from anything that supplies electrical power and they convert that power quite effectively. Solar and wind.

Following the chain of energy conversions and losses and recaptures in the chain can be very daunting and one feature is as mentioned EVs capture power that is most often off peak.

They are a good fit with a partial wind system where the power can be erratic.
The mechanical to electrical power off the wind is converted to chemical in the battery then back to electrical and then to mechanical to do useful work....drive you around.
Good EVs can recapture some of the mechanical back to electrical, then back to chemical by turning the braking system into a generator.
SuperCaps would be ideal for that as there is loss in the chemical transition and also an inability to capture the energy fast and release it fast.

Rest assured the EVs are a positive step forward in carbon reduction - so so in some areas ( coal fired grid ), brilliantly so in others. ( hydro, nuclear, wind or solar supplied areas ).

That's all well and good, macdoc, but the question here is not whether it's a good idea to drive EVs.

I'm asking a much narrower question with regard to the MPGe number on the Monroney sticker.

The blog post I linked to claims that this number is way off, and should be more in the neighborhood of 25.

It's only this particular issue that I'm asking about.

Since I have no way to evaluate the question, I'm hoping for some enlightenment that I may pass along to other similarly benighted souls who also have no way of objectively assessing such a claim.

So I cannot "forget about the miles per gallon" because that is all I'm asking about, nothing broader at all.

I'm asking for a layman's explanation of how EPA arrives at MPGe for EVs, and whether or not it's a reasonably accurate figure, or more of a stab in the dark, or (as the blog post claims) an outright "fraud".

 

[Dr. Trintignant]

I'm sortof looking for answers to these questions, you know. So simply posing them doesn't help me much, I'm afraid.

Well, my point in posing the question was simply to illustrate the complexity in coming up with a useful metric, and how--depending on which choices you make--you could come up with almost any number you wanted.

See this link:
http://www.epa.gov/air/caaac/mstrs/oct2010/1_snapp.pdf

It says "Conversion from kw-hrs to MPGe based on 33.7 kw-hrs/gallon". This is roughly the raw energy content in a gallon of gas, so it appears that that is their basis for the conversion. They don't seem to take anything else into account. The original article seems to be correct at least on that point.

You might also read this link, though:
http://www.epa.gov/fueleconomy/label/420r10909.pdf

Check out the sample labels at the end where they do some cost calculations and have to make assumptions about electricity rates and so on.

My view would be that the coal equivalent of one gallon of gasoline would be whatever mass of coal has the same potential energy, when combusted, as a gallon of gasoline.

It's roughly 4.3 kg of coal per gallon of gas. But this doesn't take efficiency in to account, and how power plants do better than cars in this regard.

If one assumes that all our electricity comes from outdated coal plants, then a "real" number of 25 MPG is perhaps reasonable. And maybe there's some West Virginian city where that's accurate. But everywhere else there is a mix of electrical generation, and so their adjusted number makes no sense there.

- Dr. Trintignant

 

[69dodge]

So are you saying that EPA does its calculations on something like the assumption that my electrical socket is actually being powered by a gasoline-fueled generator?

No. That would make some amount of sense. But, actually, the calculation assumes that your electrical socket is powered by a magical generator that is 100% efficient. That is, all the chemical energy in the generator's fuel (whether gasoline or coal or whatever) is assumed to be turned into electricity and none into waste heat. Real generators aren't like that.

 

[Dr. Trintignant]

No. That would make some amount of sense.

That makes no sense because almost no electricity is produced by small, inefficient, gasoline-powered generators.

But, actually, the calculation assumes that your electrical socket is powered by a magical generator that is 100% efficient. That is, all the chemical energy in the generator's fuel (whether gasoline or coal or whatever) is assumed to be turned into electricity and none into waste heat. Real generators aren't like that.

Why is efficiency, by itself, relevant? Waste is only important to the extent that it costs money and pollutes (the same thing, really).

But if one is concerned with cost, it's much better to look at electricity prices directly. The link authors didn't do that.

And if one is concerned with pollution, it's much better to look at the amount of pollution created per kW-h on average, taking into account pollution-free sources like nuclear or hydroelectric. The link authors didn't do that, either.

Efficiency as its own metric is absolutely useless--one may as well say that solar power is 0.0000...00001% efficient because most of the Sun's light doesn't even hit the Earth and is lost into space.

- Dr. Trintignant