Chevy Volt's "230 mpg"?


by Pengwuino
Tags: 230 mpg, chevy, volt
Pengwuino
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#1
Aug11-09, 07:47 PM
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So apparently, it's expected that the new Chevy Volt is going to get a 230mpg city rating. After reading up on it, I'm not sure how it's going to work. On a "full" charge, they expect 40 miles off pure battery. Then the engine will take over to power the generator which will have up to a 50mpg rating. Now, the devil is in the details; how does the EPA calculate mpg for vehicles like this? On a long drive, I assume the rating tends towards the rating the engine/generator would have, however in the daily grind of big city driving, I can't even imagine what it would tend towards if you keep it charged all the time (charge at home then possibly charge at work? makes me wonder if a business would charge their employees to plug in their cars :P)?

DISCUSS!

Wait, no "discuss", i just want an answer .
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Integral
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Aug11-09, 07:57 PM
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Answer 2 questions.

How far did you go?

How much gas did you use?

What else matters?

That being said they should be finding a "gas equivalence" for the charge time, then adding that figure to the gas consumed.
mgb_phys
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Aug11-09, 07:58 PM
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It's designed to meet the EPA's new rating for in-city (or the EPA's new rating is designed for this). You are allowed to start with a full charge and then use the IC when the charge runs out for the last few ( 10 ? ) miles.
So if you make a hybrid with 10% more electric range it looks like you do twice as many miles/gallon.
It's currently being ridiculed all over the net - with people claiming that their SUV does infinite mpg if you only count the 40miles downhill.

junglebeast
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Aug11-09, 08:51 PM
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Chevy Volt's "230 mpg"?


Ok...so in other words,

Gallons used = max(0, miles traveled - 40) / 50

As miles traveled goes to infinity, miles per gallons goes to 50.

This car gets 50 MPG. Not 230.
Pengwuino
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Aug11-09, 09:04 PM
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Quote Quote by junglebeast View Post
Ok...so in other words,

Gallons used = max(0, miles traveled - 40) / 50

As miles traveled goes to infinity, miles per gallons goes to 50.

This car gets 50 MPG. Not 230.
Now there's the problem, that's miles traveled continuously. The ideal situation is you drive to work, run some errands, come home, plug back in, all hopefully within that first 40 miles of pure electricity and you effectively divide by zero. The Volt violates the laws of math!!!
junglebeast
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Aug11-09, 09:08 PM
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Quote Quote by Pengwuino View Post
Now there's the problem, that's miles traveled continuously. The ideal situation is you drive to work, run some errands, come home, plug back in, all hopefully within that first 40 miles of pure electricity and you effectively divide by zero. The Volt violates the laws of math!!!
Miles per gallon is a ratio. The amount of gas used over time is a graph. The ratio they give should be the same ratio as this graph. Any adjustment in the first few miles is irrelevant in the long term. They should take a hint from Big-O notation / complexity analysis.

If they want to advertise better gas mileage, they should do it honestly: it is 40 free miles + 50 mpg after that. Saying that it has 230 miles per gallon is flat out lying, and should make them liable to class action lawsuit IMO.
Alfi
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#7
Aug12-09, 06:48 AM
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If I start with a full charge and one liter of gas. Drive till I can't go any further.
It is true that I just look at the odometer and say I went x Kilometers on one liter of gas.

But I will get a different number if I want to go from a to b ( 600km ) in a single trip.

Either way, It's a whole lot better than any other car out there.
Kurdt
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Aug12-09, 07:03 AM
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I remember when reading about the tesla roadster that they said it had equivalent mpg. Here is the wiki article about the tesla and equivalent MPG.

http://en.wikipedia.org/wiki/Tesla_R...ent_efficiency
Moonbear
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Aug12-09, 10:49 AM
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This is one of the problems that arises with trying to compare fuel efficiency when you're using two different fuels, each of which is measured in different units. The same problem will arise in trying to compare different electric-only vehicles, though. The amount of electricity used to get from A to B seems the best measure, but here you can already see with the Volt they aren't telling you that. They are instead telling you how many miles you can go on a full charge. That would be like saying the big F250 pickup truck with dual gas tanks has the same fuel efficiency as the Honda Civic because they can go the same distance before stopping to refuel.

I think the most honest answer is that GASOLINE gets you 50 mpg, which isn't that bad even on it's own. If you run out the batteries without any opportunity to stop and recharge, you can get another 40 miles.

On vehicles that get plugged in, once people start plugging them in and watching their electric bills rise, they are also going to also want some real numbers on how much electricity it takes to charge those batteries in KWh so they can figure out how much it costs per recharge based on their electric rates. Here and other places where I've seen this car discussed, I keep hearing the phrase, "The first 40 miles is free," but that's not true either. Afterall, it does cost something for the electric to charge those batteries to go that first 40 miles. And, how "green" those first 40 miles are highly depends on how the electric is generated in your area.

Afterall, what people really want out of these numbers is the answer to "How much will it cost me to operate this car the way I intend to use it?" How much will you be spending each month if you use it for your commute back and forth to work? With these types of cars, you can't just multiply mpg by the number of miles you commute. You need to factor how far electric will get you and how far gas needs to get you, and a lot of that also depends on the speeds you need to drive as to how much the gas engine needs to start contributing, and how far you need to get before you can plug it back in. If you have a 10 mile commute on back roads, that's going to be very different than if you have a 60 mile commute mostly on interstates, and not just because of the distance driven, but because of the relative contributions of electric vs. gas.

As hybrid and electric cars become more popular or common, it's going to be very important to revise the way fuel efficiency is measured and apply a standard that allows more reasonable comparisons between cars and that keeps manufacturers honest.
mgb_phys
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Aug12-09, 10:56 AM
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I think people will just ignore the consumption figures, they only have a very limited relationship to your real driving anyway.

It's only in the US that city/highway figures are even quoted or used by consumers - in Europe where gas costs $8-10/gallon nobody reads them, you just look at the engine size. You know if you bought a 3.5L BMW you aren't going to care about the cost of gas, if you are worried you buy the 1.2L Lupo instead of the 1.4L Golf - if you buy the 1L Citroen diesel your main worry is forgetting where the filler cap is when you do run out.

I think people who do manage to just use a hybrid over it's plugin range are going to be very happy about the cost.
If you believe the makers figures for the volt a 9kWh charge will do 40miles, at 10c/unit (overnight off-peak rate) you are talking about a couple of cents/mile half of the cost of even 50mpg gasoline.
Ivan Seeking
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Aug12-09, 02:30 PM
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The fact is that the increased cost of the plug-in over a standard fuel-efficient vehicle is more than the lifetime cost of fuel for the latter.

With a unit production cost to GM of about $35,000, suggesting a sales price of about $40K, at least for now, this car is way too expensive to be of any practical value. It is a novelty for yuppies.
Alfi
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Aug12-09, 02:44 PM
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Quote Quote by Ivan Seeking View Post
The fact is that the increased cost of the plug-in over a standard fuel-efficient vehicle is more than the lifetime cost of fuel for the latter.

With a unit production cost to GM of about $35,000, suggesting a sales price of about $40K, at least for now, this car is way too expensive to be of any practical value. It is a novelty for yuppies.
The atomic bomb is NOT practical. But how many Billions got wasted on that?
This car is a good start. The Idea is Well worth developing.
Such as the Wright Bros. first plane was.
Ivan Seeking
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Aug12-09, 02:54 PM
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Quote Quote by Alfi View Post
The atomic bomb is NOT practical. But how many Billions got wasted on that?
This car is a good start. The Idea is Well worth developing.
Such as the Wright Bros. first plane was.
I wasn't dissing the approach, just the current product. Very few people are going to buy a $35,000 [after federal tax credit] Corolla.

Of course, effectively lying about the mileage and saying it gets 230mpg will help for a short time - a wow factor for the suckers.
mgb_phys
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Aug12-09, 03:01 PM
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The top 113 fuel efficent models in the UK do better than 50mpg-US combined.

These aren't Smart microcars, they are mostly 90+Hp turbo diesel hatchbacks.

For some strange reason none of these seem to be available in the US/Canada, even though some of them are built by an American company.
Seat and Skoda aren't familar in America - they are basically rebadged VW Polo/Golf


Maker Model Urban Highway Combined (mpg US)

SEAT Ibiza 1.4 TDI 48.0 73.5 61.9
Volkswagen Polo 1.4 TDI 48.0 73.5 61.9
Mini MINI 50.0 67.2 60.3
Citroen C1 1.4HDi 44.4 69.2 57.4
Mini MINI R55 48.0 65.4 57.4
Skoda Fabia 1.4 TDI 44.4 69.2 57.4
Fiat 500 1.3 16v 44.4 65.4 56.0
Ford Fiesta 44.4 67.2 56.0
Ford Fiesta 1.6 TDCi 45.2 65.4 56.0

Anyway to format tables here?
Alfi
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Aug12-09, 03:03 PM
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Sorry to come across so strong.
It seems to me a lot of negatives are being expressed and not enough 'it's a good start' type of expressions.
I disagree with false advertising as well.
I do agree with the idea of getting away from oil addiction, and therefore support many efforts in electric car ideas.
Screw status symbols, screw high speed performance. I want to see practical.

:)
skeptic2
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Aug12-09, 03:04 PM
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It seems to me there are two different figures that are of interest here.

1. How much CO2 does a coal or gas fired power plant produce to generate enough electricity to charge batteries to go 50 miles compared to a gallon of gas.

2. How much does the electricity required to charge the batteries enough to drive 50 miles cost compared to a gallon of gas?
mgb_phys
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Aug12-09, 03:14 PM
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Quote Quote by skeptic2 View Post
1. How much CO2 does a coal or gas fired power plant produce to generate enough electricity to charge batteries to go 50 miles compared to a gallon of gas.
If we assume 9kWh/40miles for the Volt.
A US coal fired power station produces about 1kg CO2/kWh.
So 40miles = 1 charge = 9kg CO2
A gasoline engine releases about 2.2Kg CO2 / litre = 18.3 kg CO2/gallon(US)
So if it does 50mpg, it is about 2x as much CO2 on gas as on plugin

2. How much does the electricity required to charge the batteries enough to drive 50 miles cost compared to a gallon of gas?
A unit of electric costs around 10c, so around $1 per 40mi charge, 40miles on ICE would take around 1 gallon = $2-3 ?
mgb_phys
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Aug12-09, 03:22 PM
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Quote Quote by Alfi View Post
It seems to me a lot of negatives are being expressed and not enough 'it's a good start' type of expressions.
Thats the debate.
Is the current generation of hybrids a pointless diversion from just driving small efficent turbo diesel (european style) cars?
Or is it a first step toward a clean cheap electric vehicle?

Since 50% of US grid power comes from coal, and coal+electric is only about 50% the CO2 emission per km of gasoline is this a big saving?

Then there is the current range of hybrids available in the US.
If you are cynical they are a deliberate attempt to make electric look bad, 2x the price of a regular car, limited battery life, poor efficiency on gas. Just enough to keep the government off their backs with one hand while convincing everybody to keep buying Jeeps with the other.
If you are feeling more generous they are a 'toe in the water', small production run status symbols to get people used to the idea and to build technical knowledge for the next generation.


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