Quantifying the Volt MPG

[malcolm]

EPA vs the Chevy Volt: Hybrid or electric car? 48mpg or 100mpg? - AutoblogGreen

I think the per- trip statement of 40 miles electric and 48mpg thereafter is also the clearest way of explaining how this car works.

Much clearer than all this:-

Electronic Code of Federal Regulations:

 

[vfx]

I agree on the clarity of 40 E miles, then 48 MPG

Perhaps use that in the big bold print with a bottom-of-the-page chart that talks about Watts per mile.

 

[Joseph]

Here is what I posted at ABG

"The EPA rated an EV's mpg by mpg equivilant. Do the same for cars like the Volt; you just need to add the gallons of gasoline used to the "gallons" of gasoline equivilant used.

So, the Volt uses something like 10 kwh for a 40 mile journey. Since a gallon of gasoline holds the equivilant to about 33kwh, that means the Volt used about a third of a "gallon" to travel forty miles.

That means it gets around 120 miles per "gallon."

Now, (according to the information provided in this blog post) the EPA test is 46 miles, leaving 6 miles not in EV mode.

Let's suppose that the car gets 50mpg in this mode. That would mean that 85% of the test is 120mpg and 15% of the test is 50mpg.

For the first forty miles you would use 1/3 a gallon of "gasoline" and .12 gallons of actual gasoline for the remaining six miles. So....forty six miles and .45 gallons of gas.

That comes up to the grand total of 102 miles per gallons equivilant.

So, assuming my math is correct, the EPA rating for the Volt (in my opinion) should look something like this:

FULLY CHARGED

City: xxx mpg equivilant

Highway: xxx mpg equivilant

Combined: 102 mpg equivilant

EMPTY/HYBRID MODE

City: xx mpg

Highway: xx mpg

Combined: 48 mpg"

The EPA also used watt-hours per mile as way of measuring an EVs consumption, but I think that mpg equivilant is much better because that gives the consumer a much better feel for just how efficient an EV is. A gasoline vehicle's mpg is essentially energy consumed (x gallons) over miles (x miles) therefore x miles per gallon. For an EV (or PHEV in this case) it should be no different. You just need to convert the electrcity into "gallons."

 

[doug]

I'm gonna have to agree with malcolm and vfx, and disagree with Joseph. The MPGe calculation has already become overly convoluted as was discussed here, http://www.teslamotorsclub.com/tesla-roadster/1280-mpg-equivalent.html. Mixing that with actual MPG just adds to the confusion.

 

[stopcrazypp]

I'm gonna have to agree with malcolm and vfx, and disagree with Joseph. The MPGe calculation has already become overly convoluted as was discussed here, http://www.teslamotorsclub.com/tesla-roadster/1280-mpg-equivalent.html. Mixing that with actual MPG just adds to the confusion.

I agree, all that is needed is kWh/100miles for the EV mode (as it is done on other EVs) and the mpg for the hybrid mode. The EV range should also be included. That is basically all the information you need to do all the calculations you want. MPGe is only for CAFE considerations. With PHEVs, MPGe is just too convoluted because it changes so much depending on how many electric only miles you travel compared to the gasoline miles.

 

[Joseph]

How about both then? The sticker can tell you:

1. mpg equivilant fully charged

2. wh/mile fully charged

2. mpg not charged

The only problem might be that it is too confusing. Then again, a car window sticker already includes alot of information, so it shouldn't matter.

 

[malcolm]

Well it's safe to assume that some auto marketeers will choose to promote the figures which make the boldest claims. So we can expect a variety of misleading numbers come 2010/11.

It was interesting to note that Tesla aren't doing this. In the recent Fifth Gear TV test drive, Vicki Butler Hederson quoted the old 135 mpg number rather than the inflated/legislated 256 figure.

I hope they can maintain this.

 

[vfx]

Knowing our Government, I'm betting the final numbers will be confusing...

 

[Kardax]

I think Volt-like vehicles should get 2 numbers:

City Electric Range
Highway MPG

That provides the most meaning to potential customers, as it represents the most likely scenarios where each mode would activate.

-Ryan

 

[Miller]

EPA confused by Chevy Volt's fuel economy | Car Tech: An automotive blog from CNET - CNET Reviews

 

[malcolm]

Hi and welcome to TMC, Miller.

Thank you for the link.

Edited to Add:

GM still seem to be having problems with their acronyms. First we had the REEV, then the E-REV and now it seems to be the ER-EV (which actually makes more sense):-

GM confirms plans to sell ER-EVs in Europe in 2011, 50 Volt prototypes this fall - AutoblogGreen

Maybe it should include a question mark. As in Er......EV? :biggrin:

 

[doug]

Don't see what these guys are so confused about:

Edmunds - No "Revolting" the Volt: Chevy Battery Does Not Recharge While Driving


2011 Chevrolet Volt: Chevy Volt Engine Won't Recharge Batteries While Driving; Just A Regular Plug-In Hybrid?

.

 

[vfx]

Another thing the writers and commenters to date missed was that this system is better for the batteries. Less cycling (charging depleting -repeat) means longer life.


edit: Ok I did.

 

[vfx]

Don't see what these guys are so confused about:

Edmunds - No "Revolting" the Volt: Chevy Battery Does Not Recharge While Driving


2011 Chevrolet Volt: Chevy Volt Engine Won't Recharge Batteries While Driving; Just A Regular Plug-In Hybrid?

.

Over at Martin's blog Chris wrote and Martin responded:

Seems that the Chevy Volt story changes almost daily, and not for the better. This quote is from a story on CNN:

“GM initially said the Volt would be able to run 40 miles on its lithium-ion batteries, with a small internal combustion engine recharging the batteries to extend the range hundreds of miles. A top executive said the same thing as recently as last week.

But company spokesman Rob Peterson said Wednesday that engineers changed the design so the Volt engine will power a generator that would run the electric motor after the batteries are depleted. A small amount of power from the generator will recharge the batteries, but most will be used to directly run the car, he said.

He said bypassing the batteries is more efficient, and GM did not intend to deceive people by maintaining that he motor would only be used to recharge the batteries.

“At the end of the day, to the consumer, the vehicle will operate much the same way,” he said.”

GM to build $370M engine plant in Flint, Mich. - Sep. 25, 2008

By 2010 it will be a 6.5 litre V8 that gets 9 mpg!

All the best,

Chris H.

Martin sez:

Wow, that is really bad news. I have been so hopeful that GM would make a comeback with the Volt. This new millivolt is not going to do it for them.

I am going to bet they are having battery problems.

Comment by Chris Harvey September 25, 2008 @ 4:12 pm

 

[Cobos]

Huh ? I fail to see how this "change" is a problem? They will make sure you can plug it in as much as possible and that you will spend the least amount of gas. How can this be a problem? It's still an EV. It either works as a pure BEV for the first 40 miles and then works similar to a diesel-electric train driveline. Though in this case for the Volt as a E85/gas-electric instead. This sounds like the GOOD option if the other one was burning more gasoline through the generator arriving at home with a 100% battery. If my commute each day is a total of 60 miles I want to make sure I recharge during the night and then the last 20 miles on the way home the generator kicks in. It just uses enough fuel for me to get me home and recharge again for cheap electric driving from the grid.

Cobos

 

[doug]

What?? So even Chris and Martin are confused by this? They probably just didn't spend the time to read behind the reporter sensationalism.

From what I can glean from these stories, GM is designing the Volt to do exactly what it should. These reporters are not engineers. They have it stuck in their heads how standard (Prius type, non plug-in, parallel) hybrids work, and they think that's the way it should work. Maybe there is something to this "E-REV" nomenclature, since the public seems to think there's only one way a "hybrid" should work.

Edmunds suggests that after that first 40 miles, the Volt's battery is useless -- 400 lbs of dead weight. That's ridiculous. They seem to forget the Volt's battery is only allowed to charge as high as 80% and discharge to 30%. So after you're down to 30% the generator kicks in, keeps you going on the road and and maintains the battery to 30%. That means it uses some battery power when needed (e.g. hill climbing, hard acceleration) and puts some energy back into the battery during regen. When you get home, you get another 40 miles from the grid, not from your gas tank. This is how a plug-in serial hybrid should work.

Have to say that this sort of thing kind of annoys me. Sensationalistic headline about some recently discovered "drawback." It's just like the "Tesla Roadster Will Take 30 Hours to Charge, OMG!!!" headlines from a while back. The real story is the reporters' lack of understanding, not what's in the article.

 

[TEG]

I'm with Doug, but I am trying to stay away from all the Volt debates in general.

 

[doug]

Looks like Autoblog is on top of it. I sent them a message asking them to do an article to straighten this mess out. I got permission to post the editor's response to me:

We completely agree and haven't reported on it until now because we felt Inside Line and others were just kicking up dust and confusion where there really wasn't any, and in effect trying to catch GM doing something it wasn't.

Inside Line published a new piece today with clarification from GM that the Volt's generator will charge the battery pack, just not all the way. I wrote it up for Autoblog and it should be published soon, effectively saying exactly what you said in your email, that the generator shouldn't be charging the batteries all the way, that batteries perform optimally in between an 20% and 80% charge and constantly charging them fully or depleting them fully will shorten their life.


This whole situation was caused by IL [Edmunds Inside Line], not by GM. And yes, the public needs to understand the difference between a mild hybrid, parallel hybrid and series hybrid. I think they will if the Volt gets a crazy high EPA rating over 100 mpg. It will send a clear message that this car is not just a Chevy-badged Prius.

John Neff
Editor in Chief | Autoblog.com

Here's IL's followup article which attempts to clarify, but spins their misunderstanding as a GM reversal.
As the Volt Turns: GM Exec Says Battery Will Recharge While Driving

And here's the Autoblog article:
Settle down: Volt batteries can recharge while driving - Autoblog

But now we're back to the original topic of this thread. How are they calculating 100mpg?

 

[malcolm]

GM-VOLT : Chevy Volt Electric Car Site Blog Archive Latest Chevy Volt Battery Pack and Generator Details and Clarifications

So now there's a bit more omph in the generator to recharge the pack, but we don't know by how much.

It may be that normal driving produces the same effect as was originally reported above.

"Your mileage may vary" becomes "Your recharge rate may vary"

I think Martin is right. If they implement this then driving habits as well as regen will vary recharging far more widely than the predictable rate available from the garage wall socket. They will be stressing the batteries.

I'm guessing they'll wait for the fuss to die down then revert to Plan A.

 

[stopcrazypp]

I think this kind of confusion is brought very early on by GM's own insistance that this car be called an E-REV instead of a plug-in series hybrid and then repeating that the generator will only charge the batteries (or implying that) in order to affirm the point it should be called an E-REV and not a hybrid.

I remember early on there were a bunch of people getting up in arms that this car isn't a series hybrid because the electricity from the generator isn't directly powering the motor, but I knew this would have to happen for this car to remain efficient and not to wear out the batteries.