Excel Fuel Cost Per Mile

[William Erks]

I am trying to figure out a ruff/average cost estimate per mile.  Something didn't seem right, so I though I would run it by you guys.

 

Information from myfordmobile.com

 

Trip 1: Miles Traveled: 11.2, kWh Used: 1.4, EV Miles: 6.7, Fuel Economy(MPG): 70.6, Regen Miles: 1.5

 

Trip 2: Miles Traveled: 5, kWh Used: 0.8, EV Miles: 2.9, Fuel Economy(MPG): 48.3, Regen Miles: 0.8

 

Trip 3: Miles Traveled: 4.5, kWh Used: 1.3, EV Miles: 3.7, Fuel Economy(MPG): 77.3, Regen Miles: 0.6

 

Trip 4: Miles Traveled: 11.3, kWh Used: 1.6, EV Miles: 5.8, Fuel Economy(MPG): 43.1, Regen Miles: 1

 

So my 1st Calculation is "Gallons of Gas Used":

=(Miles Traveled - EV Miles) / Fuel Economy(MPG)

I end up with 0.063, 0.043, 0.01, 0.127

 

The "Cost of Gas" was $4.11

my 2n Calculation is "Gas Cost Per Trip"

=Gallons of Gas Used * Cost of Gas(4.11)

I end up with $0.26, $0.17, $0.04, $0.52

 

3rd Calculation is "Gas Cost Per Mile"

=Gas Cost Per Trip/ (Miles Traveled - EV Miles)

I end up with $0.058, $0.085, $0.053, $0.095

 

Next I wanted to compare the cost of Electricity Per Mile

 

"Cost kWh": $0.28 from my utility SDG&E

120 volt "Efficiency" rating 60%, (1.4) 

my 1st Calculation is "Electric Cost Per Trip"

=(kWh Used * Cost kWh) * Efficiency

I end up with $0.54, $0.31, $0.51, $0.62

 

2nd Calculation is Electric Cost Per Mile

=Electric Cost Per Trip / (EV Miles - Regen Miles)

I end up with $0.10, $0.15, $0.16, $0.13

 

Comparing the 2 side by side, Gas vs Electric

Trip 1: $0.058 vs $0.105

Trip 2: $0.085 vs $0.149

Trip 3: $0.053 vs $0.164

Trip 4: $0.095 vs $0.130

 

Does this look right or am I making the wrong calculations?

 

Average Gas Cost Per mile: $0.072

Average Electric Cost Per mile: $0.137

 

[larryh]

MPG is computed over the entire trip, not just non-EV miles.  So gas used for trip 1 is 11.2/70.6 = 0.16 gallons. 120  V charging efficiency is about 72%. 

[Kybuck]

Also, EV miles are not true plug-in EV miles.  Any regen in hybrid mode counts as EV miles.  So you could start a trip with no charge on the battery and still get EV miles.

[William Erks]

Ok, changing the Gas formals to remove EV Miles

 

Gallons of Gas Used = Miles Traveled / Fuel Economy(MPG)

0.158,  0.103, 0.058, 0.262

 

Gas Cost Per Trip = Gallons of Gas Used * Cost of Gas(4.11)

0.652, 0.425, 0.239, 1.077

 

Gas Cost Per Mile = Gas Cost Per Trip / Miles Traveled

0.058, 0.085, 0.053, 0.095

 

Oddly the final results are the same

 

Next changing the Efficiency Raito to 72% (1.28)

 

Electric Cost Per Trip = (kWh Used * Cost of kWh(0.28)) * Efficiency(1.28)

0.501, 0.286, 0.465, 0.573

 

Electric Cost Per Mile = Electric Cost Per Trip / (EV Miles - Regen Miles)

0.096, 0.136, 0.150, 0.119

 

Comparing the Trips again

Trip 1: Gas $0.058 vs Electric $0.096

Trip 2: Gas $0.085 vs Electric $0.136

Trip 3: Gas $0.053 vs Electric $0.150

Trip 4: Gas $0.095 vs Electric $0.119

 

Average 0.072 vs 0.125

 

As the Regen counts as EV Miles, I am subtracting the regen miles from the EV miles.

[larryh]

You have expensive electric rates.  There is no way to separate gas miles from electric miles.  You don't know how many of the miles resulted from the combustion of gas and how many were from plug-in energy.  The car does not track that information for you.    If you want to compare gas cost per mile to electric cost per mile you will need do separate sets of trips:  one set exclusively in EV mode and the other set when the HVB is depleted.

 

Your trips are very short.  They should be able to be done completely in EV mode. 

Edited May 25, 2014 at 01:26 AM by larryh

[Kybuck]

The easiest way I've found to calculate MPGe (or in your case, $/mile) is to use the trip odometer reported distance, gas usage and electric usage.  Or, to be more accurate, amount of gas from the pump (assuming tank is always filled) and electricity from the wall (using a Kill-A-Watt or similar - using an efficiency multiplier as you did is also better than using the car data as-is).

 

For your case, multiply the gallons of gas used by the cost of gas per gallon.  Multiply the KWH of electricity used by the cost per KWH (which can be complicated if you have tiered rates or a time-of-use plan with varying rates at different times of the day).  Add those two numbers together, and divide by the total miles driven.  This will give you a value for the entire trip.

 

Regen miles reported are not super accurate, and also combine all regen miles regardless of whether the original source of propulsion being regen'd was electric or gas, so you can't accurately separate EV cost vs gas cost per mile for a trip.

 

In your math above, you appear to be calculating gas cost per mile inaccurately - you need to subtract EV (and regen miles from EV...see how this gets difficult?) from the total number of miles.  The cost needs to be divided by the "miles travelled on gas", not total miles travelled.  

[William Erks]

my goal is really to get a ruff average cost per mile, but the results thus far seem all over the place.

 

Larryh:

yes, my trips are short, the examples above were pulled form one day,  11 miles home to work, 4 miles work to lunch, 5 miles lunch to work, and then 11 miles to home, without charging

 

2 New Trips

Trip 1 charged Battery

Miles Traveled: 21.1, kWh Used: 5.3, EV Miles 18.6, Fuel Economy(MPG) 98.2, Regen Miles: 2.5

 

Trip 2: Depleted Battery

Miles Traveled: 21.1, kWh Used: 0.1, EV Miles 9.4, Fuel Economy(MPG) 45.9, Regen Miles: 2

 

Trip 1

Gas Cost Per Mile: 0.042, Electric Cost per Mile: 0.118

 

Trip 2

Gas Cost Per Mile: 0.089, Electric Cost per Mile: 0.005 (I depleted the battery but still got a .1 kWh in there some how)

 

 

KyBuck:

My understanding from observation is EV Miles is a total,

With the only spreadable stat, is coasting / Regen Braking

Thus a subtraction from EV Miles, should not be required when trying to determine cost of Gas Per Mile

Also I did start by subtracting the EV miles from the total, but oddly enough the final results were the same when not subtracting the EV miles

 

Remaining stats grouped into EV Miles after subtraction represents 

any ICE Regen and Battery usage.  Which is understandably difficult to separate

 

I think I will refill the gas tank today and then the kilo watt meter as suggested, for one week and see if I can see the average ruff cost of a mile traveled.

 

I have tier rates (SDG&E) the weighted average comes out to $0.28 a kWh, I have thought of switching over to TOU but this seems scary at $0.44 a kWh on peak, but does drop $0.16 for super off peak

[Rexracer]

Where do you live? Those are amazingly expensive electric rates! Using TOU my off peak cost is .025 per kWh, and only $.125 at peak. If i was using the average I would be paying $.068 all the time.

 

I think to simplify your calculations you should just consider what went into the battery, and what came out in gas.

 

So day 1, you traveled 32 miles (11.2 + 4.5 + 5 + 11.3). You consumed xx gallons (readout will tell you) based on 44mpg for 12 miles (what wasn't all EV) =12/44 =.273 gallons *$4.11 per/gallon = $1.122/12 miles drive = $0.0935 per mile gas cost

 

EV cost is 20 miles driven on EV alone. Charging car back up at night you likely will put in 5.7kWh (since the car only lets you consume ~80% of the 7.7kWh battery). 5.7 kWh x $0.28 per/kWh = $1.596/20 miles drive = $0.0798 per mile electric cost.

 

As you can see i made some large assumptions, that you got 20 miles of EV usage before battery was dead, that you were driving in the city and getting 44mpg in hybrid mode, etc.

 

Im not really sure, but it almost seemed like you were using the MPG figures of 48-70 for your gas, but in hybrid only mode you are not going to get those figures.

[William Erks]

I live near San Diego, Utility SD&E

 

My Tier Rates: $0.15, $0.17, $0.35, $0.037

The 1st 344kWh used is .15

The next 103kWh used is .17

The next 344kWh used is .35

Any thing remaining uses: .37

 

For me on my bills it comes out to an average of $0.28 per kWh

 

The TOU rates would be:  Super Off-Peak $0.16, Off-Peak $0.20, On-Peak $0.44

 

I'm not entirely interested in talking about SDG&E there is not much I can do about it other then switch to TOU, which would shift my cost up, do to my working hours being shifted.

 

Don't get me wrong, the car is preforming well, I was only getting 11-13 MPG with the 2005 Jeep GC

About 65% of my driving is on the freeway

 

I have installed a Kill a watt meter, and am going to track power consumption until the next fill up.

Battery range is about 16miles, with climate control set to 72, I am consistently getting 5.4kWh out of the battery

 

Their is no easy answer, in hybrid mode I was still getting 45 MPG - Gas 0.09 a mile, while in AUTO mode, it was 98 MPG - Gas 0.04 a mile and Electric was .11 a mile

 

It really comes down to, in my case is it cheaper to just run in Hybrid mode vs plugging it in, until Gas prices come up or eclectic prices go down?

[Rexracer]

How many miles are on the car? The first 1-2k my electric range was lower then it is now. BUT freeway, and running AC will definitely kill the battery range, so in that case, 16 miles sounds pretty good.

Honestly sounds like you should just run in hybrid, and probably just should have bought the hybrid instead of the Energi.

[Kybuck]

Using the EPA combined city/hwy estimates and your stated electric/gas prices:

• 100 MPGe = 2.94 m/KWH.  At $0.28/KWH, this results in $0.0953/mile.
• 43 MPG.  At $4.11/gallon, this results in $0.0956/mile.

Obviously there are other variables at play that can sway the results - if you use heavy A/C while on electric mode, you won't see anywhere near 100 MPGe.  Charging at 120V vs. 240V also impacts the efficiency of the charging.

 

If you are getting costs anywhere in the $0.05/mile range for gas, you are still calculating it incorrectly by dividing over all miles traveled, not just those traveled under gas propulsion.

 

One other thing I just noticed = 72% charging efficiency should be a multiplier of 1.39, not 1.28. (1/0.72 = 1.39).

[Energized]

I live near San Diego, Utility SD&E

 

My Tier Rates: $0.15, $0.17, $0.35, $0.037

The 1st 344kWh used is .15

The next 103kWh used is .17

The next 344kWh used is .35

Any thing remaining uses: .37

 

For me on my bills it comes out to an average of $0.28 per kWh

 

The TOU rates would be:  Super Off-Peak $0.16, Off-Peak $0.20, On-Peak $0.44

 

I'm not entirely interested in talking about SDG&E there is not much I can do about it other then switch to TOU, which would shift my cost up, do to my working hours being shifted.

 

Don't get me wrong, the car is preforming well, I was only getting 11-13 MPG with the 2005 Jeep GC

About 65% of my driving is on the freeway

 

I have installed a Kill a watt meter, and am going to track power consumption until the next fill up.

Battery range is about 16miles, with climate control set to 72, I am consistently getting 5.4kWh out of the battery

 

Their is no easy answer, in hybrid mode I was still getting 45 MPG - Gas 0.09 a mile, while in AUTO mode, it was 98 MPG - Gas 0.04 a mile and Electric was .11 a mile

 

It really comes down to, in my case is it cheaper to just run in Hybrid mode vs plugging it in, until Gas prices come up or eclectic prices go down?

 

 

For the EV calculations you should use the marginal cost not the average cost of electricity.  The marginal cost will be higher than the average cost if you are typically in tiers 3 and 4. 

 

My rates are almost as high as yours and my own results for the past 15 months confirm that using gasoline is cheaper than electricity, even when gas is in the low $4 range.  Like you, using a TOU rate would result in a much higher monthly electric bill since the punishment for using electricity during the peak hours is so severe.

 

It's pretty remarkable how efficient and cost effective the car is using just gasoline, especially considering the large portion of gasoline costs that are just for taxes. 

[fastdriver]

I live in California's PG&E territory, and I agree gas can be cheaper. I agree calculations need to be at tier 3 or 4 depending on where you actually fall. To make matters worse, you can easily take advantage of supermarket gas rewards programs via the purchase of store gift cards to knock the price down to $3/gallon or slightly below. Oh well. It still functions well as a comfortable gas car. And I still have the green carpool sticker.