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Discussion Starter · #1 · (Edited)
How much does it cost to drive the Volt on electricity (comparing it to cost in MPG)? Some simple calculations:

Watts = Volts * Amps

1440 Watts = 12 amps (for 120 volt charger) * 120V (normal 120 household voltage)

1.44 KWH = 1440/1000 (energy needed to charge the Volt for an hour using a 120V outlet)

18.72 KWH = 1.44 KWH * 13 hours (to charge the battery fully - assumes 100% efficiency)

$2.43 = 18.72 KWH * $0.13 (my cost for electricity for a KWH - not too far from the average cost)


So it costs $2.43 to go 53 miles or $ .047 per mile (Gas would be $2.60 per gallon here and cost $ .049 per mile - updated based on flyingsherpa comment)

The EPA estimates a little less mileage (perhaps based on cheaper average cost of a KWH):

50.5 miles/full charge = 2.7 miles/KWH (EPA estimate for G2 Volt) * 18.72 KWH for a full charge

What am I missing? There are claims by GM that the Volt running solely on electricity get 92 miles per gallon (close to double what I estimate). A non-plugin Prius get about 55 MPG. Is the plugin Volt really much of an improvement?
 

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You're missing an "e". It's 92 mpge, and you are not calculating mpge. Read up on it here.

Also, your cost per mile on gas is way off, I think you meant $0.049, but Volt doesn't get 53mpg on gas, so that is wrong too.
 

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The Gen 2's energy display is pretty accurate in converting KWh to MPGe. Also, I can tell you from tracking my own costs, I was spending $120 - $130 a month (depending on the price of gas) in my 2012 Cruze ECO Manual. My lifetime fuel economy for that car was 42.6 MPG after 103,000 miles when it was totalled. My 2017 Volt costs me about $45 per month to keep charged - same driving patterns and I don't use gas at all. On cross country (Denver to Boston and back) road trips my Cruze averaged about 40-42 MPG and my Volt 38-40 MPG, but because the Cruze needed 91 octane for the best driving behavior and the Volt 87 octane the Volt is actually a little cheaper to drive on these trips.
 

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You're missing an "e". It's 92 mpge, and you are not calculating mpge. Read up on it here.

Also, your cost per mile on gas is way off, I think you meant $0.049, but Volt doesn't get 53mpg on gas, so that is wrong too.
Are you sure about not getting 53 MPG on gas. Gas fuel efficiency is tied closely to speed and when I stay on secondary roads I see anywhere from 50 to 60 MPG gas. My day trip this fall across the Colorado Mountains to leaf peep resulted in 50 MPG gas, and this included the three highest paved passes in the US as well as high speed on I-70.
 

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Are you sure about not getting 53 MPG on gas. Gas fuel efficiency is tied closely to speed and when I stay on secondary roads I see anywhere from 50 to 60 MPG gas. My day trip this fall across the Colorado Mountains to leaf peep resulted in 50 MPG gas, and this included the three highest paved passes in the US as well as high speed on I-70.
Well, EPA is 42mpg for gen2. It's not fair to use the 50-60mpg that you can get by hypermiling at lower speeds to the EPA electric numbers OP is using. For consistency you should use EPA for both (or use your numbers for both... if you drive like you do to get 50-60mpg, i bet you get a lot better than 2.7 miles / kWh too).

But really, OP, MPGe is about comparing energy used per mile, not cost. Gas contains a ton of energy but most is lost as heat. MPGe takes that into account, and shows you how much more energy efficient EVs are.
 

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I am not sure on how you are doing your math.

In Canada gas is about $1.50 a liter.
There is 3.78 liters in a US gallon, now 5.68 cdn a gallon or $4.30 us dollars for 1 us gallon
The best I have received at 46 mph is 50 mpg which costs me 8.6 cents us dollars per mile to drive.

On electricity the best I have gotten on a full charge was 131 km for a usage of 14.2 kw
131 km converts to about 81 miles

electricity varies depending on total monthly consumption which maxes at about 14 cents per kilowatt
usage of 14 cents per kilowatt times kilowatts used time efficiency of about 80 percent is
14.2 times 14 cents times .80 equals $2.49 canadian or $1.90 us dollars to drive 81 miles
this costs 2.34 cents us dollars to drive per mile.

so if we compare the 8.6 cents per mile on gas to the 2.4 cents per mile us on electricity we see a 360 percent advantage of using electricity over gasoline.

if we then take the 360% electrical advantage and multiply it against our best mpg calculation which in this case was 50 mpg we effectively get approximately 180 mpg. This is very close to what my screen which presently reads.
 

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How much does it cost to drive the Volt on electricity (comparing it to cost in MPG)? Some simple calculations:

Watts = Volts * Amps

1440 Watts = 12 amps (for 120 volt charger) * 120V (normal 120 household voltage)

1.44 KWH = 1440/1000 (energy needed to charge the Volt for an hour using a 120V outlet)

18.72 KWH = 1.44 KWH * 13 hours (to charge the battery fully - assumes 100% efficiency)

$2.43 = 18.72 KWH * $0.13 (my cost for electricity for a KWH - not too far from the average cost)


So it costs $2.43 to go 53 miles or $ .047 per mile (Gas would be $2.60 per gallon here and cost $ .49 per mile)

The EPA estimates a little less mileage (perhaps based on cheaper average cost of a KWH):

50.5 miles/full charge = 2.7 miles/KWH (EPA estimate for G2 Volt) * 18.72 KWH for a full charge

What am I missing? There are claims by GM that the Volt running solely on electricity get 92 miles per gallon (close to double what I estimate). A non-plugin Prius get about 55 MPG. Is the plugin Volt really much of an improvement?
You're talking about money. The EPA rating is solely about efficiency. The relative cost of electricity and gasoline will change the relationship between those two greatly in different regions or countries.

MPGe uses the chemical energy content to compare, so one MPGe for an electric car is how far it can go on 33.7 kWh from the wall. It doesn't really have any relation to normal usage except as a tool to compare different cars.
 

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Again guys, it's NOT ABOUT COST. It's a clearly defined metric. It breaks out to be:

total miles driven / (energy of all fuels used / energy of 1 gallon of gas).

For Volt gen1 on electric we get: 38 miles / (13.3 kWh / 33.7 kWh) = 96 MPGe

EPA is 98 combined so I'm a little off on some number, but you get the idea. The 33.7 kWh is the amount of energy in 1 gallon of gas and 13.3 kWh is to fully charge a gen1 when you include charging losses.
 

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I just posted this for our Gen 1, but the potential value for you looking at your Gen 2 is how I ran the numbers.
Remember, you are working with the amount of battery capacity the car will let you use, not the overall size of the pack.

The cost of e-fuel is most certainly cheaper for us.
Our other gas vehicles get either 16 or 20 mpg in the city. (average mpg across all vehicles is 21 mpg)
So a rough comparison would be 2 gallons of gas to go 40 miles & at $2.75/ gal for a total of $5.50

2013/2014 Volts: 16.5 kWh x 66% = 10.9 kWh usable
My Volt allows me to use 10.9 kwh of energy in the pack.
So, I have to put 10.9 kwh into the pack.
I will use 85% efficiency for charging which I have measured, and I know this can go drop to 80% if ambient gets too hot or cold.
Energy required to put 10.9 kwhr back into the batteries = 10.9 kwhr * 1.15 = 12.5 kwhr
Typical Cost to fill battery pack from emtpy= 12.5 kwhr * 11 cents / kwhr = $1.375

Cost to go 40 miles using our ICE = $5.50
Cost to go 40 miles using Volt in EV mode = $1.375

So, if I was using gasoline, this cost would be $1.375 / 2 gals or 68.75 cents per gallon.
I might then say, it is like paying 68.75 cents per gallon to drive the Volt in EV mode.


Or for you Canadians, like paying 18.2 cents per liter.
 

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The Gen 2's energy display is pretty accurate in converting KWh to MPGe. Also, I can tell you from tracking my own costs, I was spending $120 - $130 a month (depending on the price of gas) in my 2012 Cruze ECO Manual. My lifetime fuel economy for that car was 42.6 MPG after 103,000 miles when it was totalled. My 2017 Volt costs me about $45 per month to keep charged - same driving patterns and I don't use gas at all. On cross country (Denver to Boston and back) road trips my Cruze averaged about 40-42 MPG and my Volt 38-40 MPG, but because the Cruze needed 91 octane for the best driving behavior and the Volt 87 octane the Volt is actually a little cheaper to drive on these trips.
Interesting observations especially since I still have a 2011 Eco manual. I discovered the same thing about octane, although I can get away with 89 or even 87 in the cold of winter.

Sorry to hear yours was totalled, I had forgotten that. Just about 80k miles on mine, but only doing 4k a year now that we have the 2018 Volt. No plans on getting rid of the Cruze. Great 2nd car, and still fun to drive a stick.

I had the usual Cruze problems early on but all covered under warranty. Only $28 spent on 1 repair out of warranty that I performed myself. A common cooling system leak, requiring replacement of the coolant outlet on the engine.

The cost and efficiency numbers you gave make sense based on my experience.

Sent from my SM-G930V using Tapatalk
 

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Discussion Starter · #12 ·
I also think the 18.72 kWh number is wrong. Isn't that the battery's nominal capacity? The amount actually in use that can be recharged is less.

I think it is more like 16.5 including charging efficiency.
Perhaps the 18.72 kWh is wrong but the 13 hour charging period at 120V seems to say it is theoretically correct.
Perhaps someone on the site has tested this and knows the exact figure for a new Volt G2 battery.
 

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Discussion Starter · #13 ·
Again guys, it's NOT ABOUT COST. It's a clearly defined metric. It breaks out to be:

total miles driven / (energy of all fuels used / energy of 1 gallon of gas).

For Volt gen1 on electric we get: 38 miles / (13.3 kWh / 33.7 kWh) = 96 MPGe

EPA is 98 combined so I'm a little off on some number, but you get the idea. The 33.7 kWh is the amount of energy in 1 gallon of gas and 13.3 kWh is to fully charge a gen1 when you include charging losses.
I was certainly WRONG about what MGPe means. It would be nice if a figure that measures efficiency (MPGe) were a figure that easily translated into cost in MPG but the two have no clear relationship i.e., there is no way to derive one from the other. I think most people are more interested in comparing cost/mile in battery/electric versus ICE cars than in this MPGe figure.

The EPA could have chosen an average cost of a kWh, average speed, average driving ratio city/highway, etc. and come up with a cost/mile value for comparing cars. It would be much more useful IMHO.
 

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I was certainly WRONG about what MGPe means. It would be nice if a figure that measures efficiency (MPGe) were a figure that easily translated into cost in MPG but the two have no clear relationship i.e., there is no way to derive one from the other. I think most people are more interested in comparing cost/mile in battery/electric versus ICE cars than in this MPGe figure.

The EPA could have chosen an average cost of a kWh, average speed, average driving ratio city/highway, etc. and come up with a cost/mile value for comparing cars. It would be much more useful IMHO.
Not only do cost of electricity and cost of gasoline vary widely in different countries but they do with in the United States alone. Any cost averaging would be meaningless unless you just happened to be an area that was "average".
 

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I was certainly WRONG about what MGPe means. It would be nice if a figure that measures efficiency (MPGe) were a figure that easily translated into cost in MPG but the two have no clear relationship i.e., there is no way to derive one from the other. I think most people are more interested in comparing cost/mile in battery/electric versus ICE cars than in this MPGe figure.

The EPA could have chosen an average cost of a kWh, average speed, average driving ratio city/highway, etc. and come up with a cost/mile value for comparing cars. It would be much more useful IMHO.
But what power price do you use? Free overnight real time pricing in the Midwest? Forty cents per kWh in California upper tier? Eleven cent national average? Seventeen cent typical for east coast non time of use?

What about solar? For under ten grand you can buy a solar system that will cover any reasonable amount of driving...

Costs to charge can easily vary by an order of magnitude, so it's hard to do something that's actually meaningful with it. IMHO, reducing variables and providing a consistent, comparable number for efficiency was the right choice for the EPA. They did try to help with the other part with their estimated annual cost of fueling...
 

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I was certainly WRONG about what MGPe means. It would be nice if a figure that measures efficiency (MPGe) were a figure that easily translated into cost in MPG but the two have no clear relationship i.e., there is no way to derive one from the other. I think most people are more interested in comparing cost/mile in battery/electric versus ICE cars than in this MPGe figure.

The EPA could have chosen an average cost of a kWh, average speed, average driving ratio city/highway, etc. and come up with a cost/mile value for comparing cars. It would be much more useful IMHO.
Well, the EPA is interesting in protecting the environment (in theory), so reducing energy consumption is a good metric for them. I agree that consumers care about cost, but costs vary so widely... I know some people on these forums who pay nothing for overnight electricity, some pay 6 cents / kWh during the day, and some pay 40+ cents. In my area I pay about 25, but there is a TOU plan I could get (if I wasn't renting) that would make it half that. For gas, some pay $2.50 per gallon, and some pay close to $6 / gallon. Comparing cost for two sources of energy with widely disparate prices with one metric is not feasible. The way you did it is very good, break down cost per mile for your local numbers, but it's true that the average consumer may not know how to do that, unfortunately. I swear I've seen some tools online that will do it for you, though I just tried to find one and couldn't put my hands on it...

Edit: And Walter beats me to it twice in a row... I quit ;)
 

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Perhaps the 18.72 kWh is wrong but the 13 hour charging period at 120V seems to say it is theoretically correct.
Perhaps someone on the site has tested this and knows the exact figure for a new Volt G2 battery.
The default level 1 charging is 8 Amp mode.
8 amps x 120 Volts = 960 watts
960 W x 13 hours = 12.48 kwHr

A level 1 set to 12 Amp mode
12 amps x 120 Volts = 1440 W
1440 W x 13 hours = 18.72 kwhr
 

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I was certainly WRONG about what MGPe means. It would be nice if a figure that measures efficiency (MPGe) were a figure that easily translated into cost in MPG but the two have no clear relationship i.e., there is no way to derive one from the other. I think most people are more interested in comparing cost/mile in battery/electric versus ICE cars than in this MPGe figure.

The EPA could have chosen an average cost of a kWh, average speed, average driving ratio city/highway, etc. and come up with a cost/mile value for comparing cars. It would be much more useful IMHO.
I agree the definition of mpge is confusing; 33.7 kwh = 1 gallon of gasoline's energy content. But you always lose more than 50% of the energy to heat when converting a gallon of gasoline to motion. And 33.7kwh costs more than one gallon of gasoline; typically more than twice one gallon of gasoline. And 106mpge gen2 Volt is also typically more than twice a car's gasoline car's mpg rating.

The EPA does give a cost metric in their "annual cost for fuel" metric.
 

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The default level 1 charging is 8 Amp mode.
8 amps x 120 Volts = 960 watts
960 W x 13 hours = 12.48 kwHr
That will charge a gen1, -ish. I have measured charge from the wall many times with a kill-a-watt meter and it varies from high 12's to 13.5, sometimes more in extreme temperatures. For gen2, well we know it's 14.1 usable kWh, so a reasonable number would be 17.5-ish with charging losses. IIRC, L1 charge time for gen2 was around 12-13 hours at 12A (1.4kW) or 18-19 hours at 8A (.96kW)
 

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Discussion Starter · #20 · (Edited)
It is quite easy to create a map of average energy costs by state ("click on the state" maps are common on the internet) and put these costs in an equation to calculate energy savings (ICE versus EV) by state.

The most significant costs that vary by state are 1) the combined state and federal tax on gasoline which currently vary from $.25 to $.75 (https://en.wikipedia.org/wiki/File:Gas_and_Diesel_taxes.pdf ) and 2) the cost/kWh for different energy companies (which can be averaged by state or by county for that matter). The TOU variations can be ignored (averaged in).

This might require some effort but it is nothing compared the complexity of something like Google Maps or even a GPS navigation box in your car. The claim that there are just too many variables seems incorrect.

It would also have the added advantage of documenting which states (or counties) are EV-friendly versus those that are not.
 
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