Chevy Volt's "230 mpg"?


by Pengwuino
Tags: 230 mpg, chevy, volt
mheslep
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#55
Aug13-09, 07:59 PM
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Quote Quote by Kenneth Mann View Post
For the Volt:
2) miles per kwh equivqlent to 230 mpg when running on battery
You do not want to do that 'mpg' 'equivalent' bit on the battery. Its hopelessly misleading. Can you travel 230 continuous miles with one gallon in the tank? No. On batteries then? No. Does the gallon of gas cost the same as the same equivalent energy placed in the battery from a wall plug? No.
mheslep
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#56
Aug13-09, 08:05 PM
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It occurs to me that GM knows full well their recent release of the '230 mpg' figure would be controversial, confusing, and would be challenged. I also believe that's exactly what they want. They need people to start talking about this car, to get this very new thing into the daily discussion. We've been obliging them nicely. More than a few people will try out controversial new things, but very few people will try out something they've little or never heard of.
Kenneth Mann
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#57
Aug14-09, 06:37 PM
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Quote Quote by mheslep View Post
You do not want to do that 'mpg' 'equivalent' bit on the battery. Its hopelessly misleading. Can you travel 230 continuous miles with one gallon in the tank? No. On batteries then? No. Does the gallon of gas cost the same as the same equivalent energy placed in the battery from a wall plug? No.
Maybe there is desire not to do that by some - - it is done - - by EPA. It is obviously confusing, judging from the confusion that has occurred in this string - - but it is perfectly valid. There is no general derivational relationship to MPG (equivalent or not) that requires driving a certain number of miles. Battery capacity of the Volt limits its 230 MPG capability to 40 miles. After that, economy drops to 50 MPG (using gasoline).

KM
Kenneth Mann
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Aug14-09, 06:39 PM
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Quote Quote by mheslep View Post
GM claims 50 mpg.
The generator is small, 70HP, running near constant RPM, so 50 mpg is doable.
http://gm-volt.com/chevy-volt-faqs/
Thanks, I didn't check it.

KM
Kenneth Mann
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#59
Aug14-09, 07:44 PM
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Just to hint at how confusing the equivalent mileage can be, if both battery and gasoline economies are combined, I've figured a few examples. The only quick-and-easy cases are those of runs of under forty (40) miles, for which cases, the economy will always be 230 (equivalent)MPG. Once the travel goes over 40 miles (approximately), the MPG gets incrementally lower.

Take, for example, a travel of 50 miles from start (full charge):
For the first 40 miles, we get:
40 Mi/230 MPG = 0.1739 Gal (equivalent)
For the next 10 miles, we get:
10 M/50 MPG = 0.2 Gal
For the full 50 miles:
50 M/0.3739 Gal = 133.7 MPG

For a 60 mile run from start:
60M / .5739 Gal = 104.5 MPG

For a 90 mile run from start:
90M / 1.1739 Gal = 76.6 MPG

For a 240 mile run from start:
240M / 4.1739 Gal = 57.5 MPG

I hope this gives some idea of what to expect from the Volt. Obviously unless you average nearly 250 miles driven per day, the turbo diesel won't beat it in economy (until someone puts out a serial hybrid turbo diesel).
The Prius simply won't match it in economy.

KM
Phrak
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Aug14-09, 08:07 PM
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Quote Quote by Kenneth Mann View Post
Just to hint at how confusing the equivalent mileage can be, if both battery and gasoline economies are combined, I've figured a few examples. The only quick-and-easy cases are those of runs of under forty (40) miles, for which cases, the economy will always be 230 (equivalent)MPG. Once the travel goes over 40 miles (approximately), the MPG gets incrementally lower.

Take, for example, a travel of 50 miles from start (full charge):
For the first 40 miles, we get:
40 Mi/230 MPG = 0.1739 Gal (equivalent)
For the next 10 miles, we get:
10 M/50 MPG = 0.2 Gal
For the full 50 miles:
50 M/0.3739 Gal = 133.7 MPG

For a 60 mile run from start:
60M / .5739 Gal = 104.5 MPG

For a 90 mile run from start:
90M / 1.1739 Gal = 76.6 MPG

For a 240 mile run from start:
240M / 4.1739 Gal = 57.5 MPG

I hope this gives some idea of what to expect from the Volt. Obviously unless you average nearly 250 miles driven per day, the turbo diesel won't beat it in economy (until someone puts out a serial hybrid turbo diesel).
The Prius simply won't match it in economy.

KM
You used their 230 mpg figure, which is questionable.

From previous calculations, I assume 27% efficiency for an internal combustion engine from fuel to axle. For Lithium polymer batteries, 67% efficiency from plug to axle. Use your own numbers for cost of the electric utility and gasoline, to find an mpg equivalent. I would go 10c per KWHr and $320 per gallon. You might have better numbers.
Redbelly98
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#61
Aug14-09, 08:22 PM
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Check out the last item in that faq:
Q: Will tall people fit in it?
A: Bob Boniface, chief of Volt design says the car is being designed to accommodate drivers from 5th percentile females up to 95th percentile height males.
So the car will accommodate 95% of women and only 5% of men? That means the car would be marketed primarily for single women. Or am I misinterpreting this statement?
lisab
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Aug14-09, 08:35 PM
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Quote Quote by Redbelly98 View Post
Check out the last item in that faq:


So the car will accommodate 95% of women and only 5% of men? That means the car would be marketed primarily for single women. Or am I misinterpreting this statement?
I interpret that to be: the car will fit all but the shortest 5% of women, and all but the tallest 5% of men.
russ_watters
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Aug14-09, 08:36 PM
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That's a height range. A 5th percentile female is near the shortest and a 95th percentile male is near the tallest. In other words, it will fit 95% of all people.
Redbelly98
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Aug14-09, 08:58 PM
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Quote Quote by lisab View Post
I interpret that to be: the car will fit all but the shortest 5% of women, and all but the tallest 5% of men.
Quote Quote by russ_watters View Post
That's a height range. A 5th percentile female is near the shortest and a 95th percentile male is near the tallest. In other words, it will fit 95% of all people.
Okay, that makes sense. :slappinghead: Thanks to you both.
Kenneth Mann
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#65
Aug15-09, 12:44 AM
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Quote Quote by russ_watters View Post
Again, that's not what is apparently being claimed. The link I posted and the analysis someone else did imply that that is gas consumption while running in a mostly electric mode.
I don't know what this "mostly electric" mode is. The Volt is a serial hybrid, and as such should either operate as "all from battery" or from "electricity generated" from the gasoline. I suppose that the system could operate from electricity coming from both the generator and the battery, but what would be the point of this? This would simply reduce the overall efficiency from that gained if running totally from battery. The only purpose of this would be either to make up for the inadequacy (current capacity) of running from battery - - or to obfuscate the true operational cost (by ignoring that derived from battery - - a cynical assumption).

KM
Kenneth Mann
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Aug15-09, 12:53 AM
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Quote Quote by russ_watters View Post
The EPA will just have to make a standard and have car companies stick to it. They already have a driving course for city and highway driving for other cars, so there is no reason they can't set up a similar standard for hybrids/plug-ins.

Perhaps to reflect the fact that people who commute tend to commute less than 40 miles a day, they will need to add another couple of data points, for "city commute" and "highway commute".

Or perhaps they could even do a customize fuel economy report for everyone. Fill out an online questionaire about your driving habits and it could give you your predicted fuel economy with different cars.
Good luck! (Now I'm being cynical, but this just doesn't seem likely.)

KM
Kenneth Mann
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Aug15-09, 01:01 AM
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Quote Quote by Phrak View Post
You used their 230 mpg figure, which is questionable.
Why do you question it? If the number came from Honda would you question it? If it is incorrect, approximately what should it be, and why.

KM
Ivan Seeking
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Aug15-09, 02:28 AM
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Quote Quote by mheslep View Post
While I feel the argument for the EV is stronger, your post is one of the better articulated one page comparisons of the two competitors Ive seen lately, and there are many lesser ones to see.

This part is particularly interesting so two responses here.

First I'd argue that the problem with a 100% biofuel replacement of petroleum is that at current efficiencies of the transportation fleet biofuel crops can't handle the demand with out causing more problems along the way. I'm not inclined to rerun the miles/perBTU/per acre game one more time here; but I'll go ahead and suggest that BF at that scale requires too much land and water, inevitably displacing good land in use for something else. Now here's the big caveat: a BF takeover can work in a BTU sense if the efficiency of transportation goes up by 2 to 3x, which takes us back around to replacement of the internal combustion engine w/ the electric motor.
That is why, imo, the majority of biofuel will be produced using closed, salt-water algae systems: No competition for land or fresh water, and plenty of water. Not to mention that the ocean [or lakes when appropriate] can be used to provide natural temperature regulation, which has a high energy and or financial cost for many land-based designs. It also removes the cost of land, which is significant to the final cost of the fuel produced.

As for ideas like an electric 797, while it may be possible one day, I think we are a long way from that one. When I have a practical and cost effective electric car, we can talk.

The latest news about algae.
http://www.exxonmobil.com/corporate/..._factsheet.pdf
russ_watters
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Aug15-09, 03:00 AM
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Quote Quote by Kenneth Mann View Post
I don't know what this "mostly electric" mode is.
Probably should have said "mostly in electric mode". Ie, 40 miles on battery, 10 miles on the engine.
Phrak
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Aug15-09, 03:31 AM
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Quote Quote by Kenneth Mann View Post
Why do you question it? If the number came from Honda would you question it? If it is incorrect, approximately what should it be, and why.

KM
The energy content of gasoline is about 34 KWhrs per US gallon.
daveg360
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Aug15-09, 07:35 AM
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I think I fill the tank on my diesel once every couple of months. It's a 2 litre tank and I probably do 600 miles between fill-ups. So I reckon I get 1100+MPG.

Of course I'm talking about the screenwasher tank but it seems to be just as relevant as measuring gas mileage for a journey mostly done on power from the powerstation down the road.

(can I get my gas mileage up by pushing my car 90% of the way to work everyday?)
mheslep
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Aug15-09, 07:41 PM
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Quote Quote by Ivan Seeking View Post
That is why, imo, the majority of biofuel will be produced using closed, salt-water algae systems: No competition for land or fresh water, and plenty of water. ...
I don't see how that's feasible - a closed system on the open ocean? Certainly there's the sheltered lagoon or bay to work with, but I don't see how that scales up to the square miles that are needed.


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