Under What Conditions is the Chevy Volt’s Quoted 40 Mile Electric Range Modelled?
We have had substantial discussions about how the Volt’s 40 mile electric range is calculated. Since the car only exists in models, the 40 mile range isn’t real road conditions, but was arrived at using computer models.
People often question whether that 40 miles will be “downhill with a tailwind” and no AC or headlights, or whether it will be true in real-world driving situations.
As this number is very significant from a marketing and PR standpoint, I would think GM is likely being pretty conservative in this estimate, although some commenters suspect they might be putting their best foot forward.
I decided to ask those people at GM who are integral to the E-Flex program and here is their response:
GM-Volt: Is the 40 mile all-electric range a MAXIMUM, or is it based on one of the EPA driving profiles?
GM: The 40 mile range is modelled on the EPA city cycle (federal test procedure) - and the 40 miles is our target for battery END OF LIFE. The EPA city cycle includes a range of starts, stops and accelerations.
So it looks like they mean we should get 40 miles electric in real-world city drives folks, although from my prior GM discussions, they do mean with the A/C off.
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44 Responses to “Under What Conditions is the Chevy Volt’s Quoted 40 Mile Electric Range Modelled?”
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October 22nd, 2007 at 7:19 am
So if this is estimated city mileage with the A/C off, what is the estimated highway mileage with the A/C off? How about with the A/C on as well?
October 22nd, 2007 at 7:35 am
I like the fact that they are stating that the 40 mile range estimate is end of life on the battery, the initial range could be noticeably higher. I wish they had mixed in highway miles and a little use of the ac and the lights, but what I really want to hear is that the battery packs that were scheduled for release and testing this month are in fact being placed in the mules and that testing has started. The timeline stated that this was the month, and I hope we hear about the testing from Lutz soon, and not some pie in the sky about hydrogen.
Lyle, Thanks for taking the time to post this information, this site is phenomenal!
October 22nd, 2007 at 8:29 am
This also begs the question of whether the car at new conditions is better than 200 watt-hours per mile. Currently it’s calculated as using 50% of the battery (80% to 30%) for a 16 kW-hr battery pack:
(0.8 - 0.3)(16 kW-hr)/(40 mi) = 200 W-hr/mi
This compares to 177 W-hr/mi for the Tesla Roadster.
So, if GM’s calculations represent end of life and assuming the car can travel 10% further at new conditions (i.e. 44 miles) then a new Volt would be almost as efficient as a new Tesla Roadster and their previous EV1. That’s a little hard to believe, but good on them.
Where things get complicated is in the charging efficiency. The Tesla is 86% efficient at battery charging. The EV1 was not very efficient at charging the NiMh batteries, so it took significantly more power from your A/C outlet to actually charge it up.
October 22nd, 2007 at 9:46 am
From a123s website their cells are at about 87% capacity at about 3600 FULL discharges(http://www.a123systems.com/newsite/index.php#/technology/life/lchart1/).
It is quite possible that by keeping these cells in the sweet spot that they lose very little capacity, though 10 years of calendar life is a big factor.
October 22nd, 2007 at 9:46 am
It does get reduced range in city driving, though, right? It’s not like a Prius with a the efficiency being inverted for city driving due to regen braking? It’s okay for me either way, but I am wondering about that.
October 22nd, 2007 at 10:32 am
From the EPA website: http://www.epa.gov/nvfel/testing/dynamometer.htm
The FTP profile cleary shows that it is testing city driving and it looks like it averages about 30 mph with peaks of almost 60. So under highway driving I would think you would get the 40 mile range at about 35mph. Based on the performance of the converted Priuses, the range at 60 mph would be about 25 miles. It would be nice if GM published the highway numbers as well.
October 22nd, 2007 at 10:56 am
Mike756, if your numbers are correct, then this is very disappointing news. Since I drive 47 miles on the highway each way to work, it will take a very very long time for me to make up the different when buying a cheap car like the Hyundai Elantra. I paid $13.5K out the door for this car. So far I have traveled 150,000 miles with it and it still runs strong and gets 31 MPG. But if the Volt comes out at $30K, I will need to buy approx. $16,000 worth of gas to break even. $160,000 minus the plug-in energy that is.
GM says that most commuters travel 40 miles p/day or less. I really wonder how many of those only travel in the city and skip the highway altogether? I would speculate that more than half drive on the highway.
If true, and the 25 miles is correct, then I don’t see how the Volt will be cost effective for me and simply have to bypass it completely. Either way, I have promised myself to wait until 2010 or 2011 to buy a new car. I will see what is available then.
But wow, I am really disappointed.
October 22nd, 2007 at 10:58 am
I didn’t realize the average speed was stated on the FTP profile.
http://www.epa.gov/nvfel/methods/ftpdds.gif
I says the average speed is 21.2 mph. I guess I was a little off. So the Volt will get 40 miles at an average speed of 21 mph. Actually, if driven at a constant speed, it will be higher since constant speed driving is more efficient, so lets say 25 mph. At typical highway speeds, I can’t see getting much more than 20-25 miles. This would be fine with me, however, given my current work commute.
October 22nd, 2007 at 10:59 am
A typo “$160,000 minus the plug-in energy that is.”
I meant $16,000
Sorry.
October 22nd, 2007 at 11:04 am
Steven B, they are quoting city driving and it will have the same regenerative braking as a prius and probably more efficient due to the lack of mechanical linkage.
October 22nd, 2007 at 11:05 am
Ohm, you can’t really compare the power consumption of a four door, four seat commuter vehicle with a two seat, light, agile roadster.
Simple physics - the Tesla Roadster is smaller and lighter, so it takes less energy to go the same distance.
I think this question being answered is good news. If the Volt can do 40 miles by the new EPA City efficiency standards… at the battery’s END OF LIFE… that’s great! End of life should be when the batteries can store about 80% of their previous useful power.
October 22nd, 2007 at 12:07 pm
My point was that the Volt compares well to the Tesla Roadster, despite being a larger and heavier vehicle. That’s what surprised me. We’ll see if they actually deliver on their computer models.
October 22nd, 2007 at 12:11 pm
Most of my driving is highway at 70 MPH. Bummer.
October 22nd, 2007 at 12:16 pm
We’re definitely going to need GM to let us know what the highway range is. But I don’t think that the numbers that y’all are generating are realistic either. 40 mile range at 25 mph constant!?! WTF, that can’t be accurate, even with regen braking. Acceleration always puts much more demand on a powerplant than cruising. We’ll have to see what GM’s estimates are. They listen to us.
October 22nd, 2007 at 12:32 pm
[quote comment="11667"]
Where things get complicated is in the charging efficiency. The Tesla is 86% efficient at battery charging. The EV1 was not very efficient at charging the NiMh batteries, so it took significantly more power from your A/C outlet to actually charge it up.[/quote]
The impedance of the A123 cells is pretty spectacular compared to that of the Tesla’s - A123 is at~8mohm, versus about 90mohm for typical cobalt 18650’s. Hence the high power density and fast recharges. With a relatively smaller pack, as well as built-in smart charging, they should have no problem getting good charging efficiency.
October 22nd, 2007 at 12:51 pm
As far as efficiency goes, I suspect 40 miles is going to be measured at optimal cruising speed. I test drove an AC Propulsion eBox this weekend, and after an entire day of hard accelerations and stop and go traffic, even with regen on max, the car was using over 300Wh/mile on average. At over 3000 pounds, the eBox probably weighs about the same as the Volt, and it had the exact same specification motor (AC induction, 120 kW).
In fairness, the car was being driven by people who didn’t have much electric drive experience, so they were constantly tapping the friction brake out of habit. With a little more careful modulation of the throttle and regen, it’s supposed to be capable of 200Wh/mile. (180 mile max range on 35kWh)
October 22nd, 2007 at 1:00 pm
“As far as efficiency goes, I suspect 40 miles is going to be measured at optimal cruising speed.”
Ok, what is optimal cruising speed?
“it’s supposed to be capable of 200Wh/mile”
At what speed?
October 22nd, 2007 at 1:54 pm
Optimal efficiency for most cars is maintaining ~55 mph on a flat surface.
October 22nd, 2007 at 2:20 pm
The prius has slightly lower highway mileage vs city. Therefore if it can go 40 miles in the city at end of life, it should go about 40 on the highway (at 55). I do about 70 so it might be less.
October 22nd, 2007 at 2:32 pm
I would cause a huge accident if I drove 55 on any of the highways around here. Anyway, highway traffic flows at 65-75mph and this requires a small fraction of the energy required to accelerate from stoplight to stoplight because regen braking is NOWHERE near 100%. Physics is why the ICE highway mileage is better than city mileage and physics is why the Volt BEV-40 with a range extender will have a greater all electric range on the highway than in the city. This is doubly true because people will love to play with the torque curve in their new Volts and jack rabbit from light to light racing each other. It’s human nature to play and show off.
October 22nd, 2007 at 2:42 pm
By the way, the Volt and the Prius are COMPLETELY different animals. Apples and Oranges. The Prius is a gasoline car with a little electric helper motor to capture and reuse breaking energy and the Volt is an electric car with a little generator as insurance in case you forgot to plug it in last night or if you’re on one of those 15% longer than 40 mile round trips. Remember, 85% of all commutes are shorter than 40 miles round trip.
October 22nd, 2007 at 2:44 pm
I read somewhere that it was supposed to get 50 mpg with the engine running. If it will get 50 mpg going 70 mph on the highway, I love that. Anything it does on the battery alone is just a bonus.
Some bloggers over at Fastlane said, if it will get 50 mpg, just give it to us now and don’t be held up waiting for the magic battery. We can plug that in if and when it becomes reality. Amen.
I guess maybe you need some kind of battery pack to capture the regen energy to make the 50 mpg. Current batery technology can do that, right? So change out later to the magic batteries.
October 22nd, 2007 at 2:55 pm
Noel, the bloggers at Fastlane are morons. The Volt needs a battery to buffer power demand of the motor which is about 200% of what the generator (as designed) can deliver.
If they want a Volt that can’t accelerate better than 0-60 in 16 seconds or so… you can have it. I don’t want it.
(120kW motor, 53kW peak generator = not very fast)
October 22nd, 2007 at 3:04 pm
As far as I know, most EV’s have their optimum efficiency at ~45mph.
For example:
1) http://avt.inl.gov/pdf/fsev/eva/ev1_eva.pdf
The NiMH EV1 used 127Wh/mile at 45mph, versus 168Wh/mile at 60mph. Combined cycle=179Wh/mile.
2) http://avt.inl.gov/pdf/fsev/eva/toyrav96.pdf
Even the big, heavy lead acid RAV4 EV got 198 Wh/mile at 45mph, versus 289 Wh/mile at60mph. Combined cycle = 235.
October 22nd, 2007 at 3:29 pm
Regen braking allows the Prius to get better city mileage than highway. If anything, the Volt will make that difference bigger, as it basically has heavier-duty regen braking. So maybe 40 MPG highway, ~32 mi range? Also, I think the EPA highway test doesn’t go above 60 or 65 MPH… it takes a lot more energy to drive 75 than 65… so the Volt may be looking at a real world highway range of around 25 miles. Disappointing.
October 22nd, 2007 at 3:37 pm
A 25 mile highway range just about seals it for me. It’s a no go for the Volt. I hope that GM will publish these numbers so that we all don’t need to speculate. Yes, 50 MPG is something to smile about, but when I can buy a really cheap, excellent working car that gets around 35 MPG, well, let’s just say that I can’t justify it to myself, never mind my wife.
October 22nd, 2007 at 3:38 pm
“Noel, the bloggers at Fastlane are morons.”
Where would we be without smart people like you Matt986 to call other people on the internet morons. People on the internet already are cruel enough. Either be part of the problem or part of the solution.
And by the way, the Volt could be sold now with current battery technology. Hybrid batteries could buffer more than enough energy for a normal user’s acceleration needs.
October 22nd, 2007 at 4:20 pm
“Physics is why the ICE highway mileage is better than city mileage and physics is why the Volt BEV-40 with a range extender will have a greater all electric range on the highway than in the city.”
The difference between city and highway for an EV is less than the difference between city and highway for an ICE for two reasons:
1. There is no idling at stop lights
2. Regenerative braking
The highway mileage will be a strong function of the wind resistance. As you can see in the pdfs provided by AES above, there is considerable difference in the wh/mi at 60mph between the EV1 and the RAV4.
Also the RAV4 uses more energy at 60mph than in the SAE J1634, while the EV1 uses less.
I don’t think it is as simple as “physics”
October 22nd, 2007 at 5:05 pm
The problem with the PFD’s is that you’ve got apples and oranges. It appears that the tested RAV 4 is with Lead-acid and the EV-1 is with Nimh.
Interesting to note that the RAV 4 tips the scales at 3300+ LBS.
October 22nd, 2007 at 5:20 pm
The battery pack is important for weight alone. The efficiency paradigm for the two electric drive trains is the same.
October 22nd, 2007 at 5:43 pm
For the 1998 RAV4 23.01 kWh of energy from the NiMH batteries were used to drive 94.0 miles of the driving cycle range, which is 245 Wh/mi.
http://ev.inel.gov/pdf/fsev/eva/toyrav98.pdf
BUT… the A/C wall outlet to wheels efficiency was reported to be 432 Wh-AC per mile. So the real test is how many BTU’s at the meter your power company will ding you for.
The 2003 RAV4 improved its numbers. If you look at the following link and do the math based on the cost of electricity they are assuming, it works out to 302 Wh/mi.
http://www.fueleconomy.gov/feg/byfuel/EV2003.shtml
I estimated the Volt to be 233 and the Tesla 206.
You can see more of my calculations here:
http://ohmexcited.googlepages.com/CO2.htm
Please feel free to punch holes in them.
October 22nd, 2007 at 6:11 pm
Thanks Mike, #26. I was trying to give the credit for the brilliant idea to the other bloggers on Fastlane. If it comes to being a moron, I guess I have to take the blame on myself, because I was just as enthused about the idea as anybody, if not more so. There are some very bright and well informed bloggers on Fastlane, by the way.
The difference in fuel consumption between 55 mph and 75 mph is why I was on about the Cd the other day. The science of aerodynamics may not have changed much since the EV1, as one blogger said. On the other hand, there is a reason why top racing teams in every series are constantly spending millions of dollars in wind tunnel rental/ownership. If the basic science hasn’t changed, the understanding of how every little detail adds up to significant advantage is the reason for unending development. It’s like Steve Smith said about the weight. One ounce at a time.
Aero is just as important to high fuel economy vehicles as it is to racing cars.
October 22nd, 2007 at 6:18 pm
Interesting white paper. However, you don’t take nuclear plants (our electricity is nuke) and the fact that the trend will be towards more solar recharging stations as CA had in the brief and anemic first life of the EV.
If this catches on, and it will, there will be many more of these (solar recharging sta.s).
October 22nd, 2007 at 6:36 pm
Rashiid Amul #25
I wouldn’t advise you to give up based on what I said. That was just a very rough guess. I just want to know what the actual numbers are. They should be able to model the highway numbers just they did for the city. I would like to see a graph or a table of the wh/mi for various speeds.
October 22nd, 2007 at 7:03 pm
Aero and weight will play a significant role in the story, and they’ve yet to be determined. 200 Wh/mile is by no means theoretically impossible.
Just to throw another number into the mix:
http://www.google.org/recharge/
Google.org’s Hymotion prius uses 120Wh/mile.
October 22nd, 2007 at 7:18 pm
120Wh/mile is not in pure EV mode. The Prius is a parallel hybrid and also burning gasoline. Note that in their calculations they add the two contributions together to estimate CO2 output:
“CO2e emissions for the plug-in hybrids in our fleet are 4,623 pounds CO2e/year for 12,000 miles or 0.385 pounds CO2e/mile. Total CO2e emissions are the sum of CO2e emissions from gasoline use and electricity use.”
Note that in the California grid, I calculated 0.205 pounds CO2 per mile for the Volt and 0.182 for the Tesla, both of which are better number than that for the plug-in Prius, despite “higher” reported Wh/mile values.
http://ohmexcited.googlepages.com/CO2.htm
So, you’re really comparing fruit salad with oranges.
October 22nd, 2007 at 9:34 pm
Ah, good catch Ohm (no need for fruit-based ad hominem though). The google.org page is a little ambiguous, since the Hymotion conversions ARE indeed capable of electric only.
This article is a little dated, but it “estimates the 5kWh lithium-ion module will deliver about 50km (31 miles) of electric-only driving range.”
So that’s ~161 Wh/mile all electric.
I’ll update if I find any better estimates.
October 22nd, 2007 at 10:55 pm
Sorry, forgot the link:
http://www.evworld.com/article.cfm?archive=1&storyid=991&first=3118&end=3117
October 22nd, 2007 at 11:49 pm
First, any mileage figure MPK, must be replenishment KWH, the number of KWHs you are charged for. To discuss internal numbers is misleading. So the RAV4 got about 2.5 MPK. The Volt should do better, perhaps 3 or 3.5 miles per KWH.
Also the end of life comment is vaporware, the car uses 8KWH of power at end of life, the reduction in overall capacity comes out of the unused 100-80 and 30-0 range.
So to back up, the 40 mile range is like the Prius getting 60 MPG city. It actually got about 45. So if we ratio it, the actual city mileage achieved may be as high as 30 miles per 8 KWH and the highway about 24 miles per KWH. That is absolutely outstanding.
As far as 1/2 the people driving over 40 miles in their daily commutes, you need to keep in mind that as the population ages and retires, many of us simply run to the store, the park, and the coffee shops. This is the dawning of the age of freeway golf carts!
October 23rd, 2007 at 5:57 am
Sorry to point this out, but do any of you have the actual specs for the Volt?!? I don’t think you do. You seem to be playing with calculators here and all without the appropriate variables for your calculations. GM said the Volt will be designed for 40 miles. Then you end up saying that it will be for 30 to 24. They are the ones developing the car and they have not released all the specs. I suggest that you wait until whoever there reads our posts gets us an actual answer and stop with conjecture. It’s interesting to find out that range is based on city cycle. It’s also important to realize that highway driving will have a significantly different number. But in the end, all driving is mixed city and highway. And if you’re driving at 70 miles per hour, you had to accelerate to get there, and when you get to your destination, you will use your regen braking when coming to a stop. Let’s just wait for GM to find out and let us know what highway AER will be and stop guessing.
October 23rd, 2007 at 7:19 am
Mike756, I won’t give up yet. I am waiting for the real numbers and realize that some of this is speculative.
Lyle, have you heard anything about the Volt tour schedule? I haven’t had much luck on the Net. Connecticut is having an International Auto Show next month and was hoping the Volt would be there. Any ideas? Thanks.
October 23rd, 2007 at 7:50 am
Steven B #40
What are we supposed to do, just say ooh and aah? You don’t think it is a fair question to ask what the highway mileage will be? I think everyone knows that we don’t have the actual specs, but they have released some numbers, i.e. the 40 mile range. However, it makes no sense to say “40 mile range” without qualifiying how that range was determined. They are going to have to release the highway mileage at some point anyway, and as a fair percentage of commutes will be at highway speeds, I think this is a fair question to ask.
October 24th, 2007 at 7:21 am
Hi Steven B, yes, my expection of actual Volt performance is based on numbers from GM. Recall the article where the power necessary to sustain freeway speed was given? I used that to calculate a 24 MPK freeway performance.
October 24th, 2007 at 10:57 pm
Rashiid,
Don’t be surprised if the cheapest high gas mileage car is more economical than the newest high-tech hybrid at first. The cost of electric drive will come down as mass-production ramps up and competition sets in from multiple suppliers. Don’t forget that you spend $k’s on gas per year if you’re driving 15,000miles/year. And gas prices are just going to go up.