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How much it is actually costing me

Discussion in 'Model S: Battery & Charging' started by wesley888, Dec 19, 2016.

  1. wesley888

    wesley888 Member

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    My wife just asked me how much it cost driving the Tesla compare to gasoline. I thought about it, but I really did not know.

    Let's say we are using 400Wh/mile in winter time with all the heat and snow and wind, and our actual electricity cost is 0.216/KWh after all the tax and fee. That's 0.4KWh/miles * 0.216/KWh = $0.0864 per mile.

    If we were to buy gasoline at $2.5/gallon. $2.5/gallon divided by $0.0864/miles = $2.5/gallon * (miles/$0.0864)
    That's only 28.9 miles/gallon. That is not an impressive number at all. Did I calculate it right?
     
  2. wesley888

    wesley888 Member

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    I just shorten my calculation to a more simple formula:

    MPGe = (Gas Price) * 1000 / (Electricity Cost) divided by your Tesla's KWH number

    In my case, $2.5 * 1000 / $0.216 / 400 = 28.94 MPGe


    IF the gas is $3, Electricity is $0.11 and the Tesla is only using 300KWh:

    MPGe = $3 * 1000 / $0.11 / 300 = 90 MPGe

    Now I see how they get the impressive number from...

    How is your actual MPGe?
     
  3. brkaus

    brkaus Active Member

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    I believe you did the math correctly.

    Not bad compared to cars of similar size/performance. But compared to a Civic, Accord, Altima it stinks.

    Your electricity rate is just under 2x the national average, which hurts quite a bit in this calculation.
     
    • Like x 1
  4. Boourns

    Boourns Member

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    Yeah your electricity is quite expensive.

    Using your formula I get about 55.8. Gas is around $2.15 right now, electricity is $0.11, currently averaging about 350kWh/mile.
     
    • Like x 1
  5. Twiglett

    Twiglett Single pedal driver

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    That is a calculation, but I'm pretty sure that isn't how they calculate MPGe
    Miles per gallon gasoline equivalent - Wikipedia
    The cost of a gallon doesn't affect MPG in any way
    I'm missing something aren't I :(
     
    • Like x 1
  6. wesley888

    wesley888 Member

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    Theirs are more internal and scientific using energy unit conversion factors, wall to wheels energy, energy contents in the gasoline, etc. Very generic and I have none of those numbers. Their method is good for coming up a single number to compare between cars, regardless you are paying $0.20 per KWh or $0.10 per KWh, which doesn't apply in real world.

    Mine is a real life equivalent of MPG. The actual money that we actual paid for, for gas, or electricity, depends on where you live.
     
  7. thefortunes

    thefortunes Member

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    As Twiglett said that is not the official MPGe calc, but yours (or the variant $/mi) is also what I use when discussing operating cost with friends because it is easily compared:

    Roadster: gas $2.15, electricity $0.06 (TOU billing), Dec-to-date 274Wh/mi = 131 eMPG. Lifetime 244kWh = 147 eMPG (at current gas price)

    Model S: gas $2.15, electricity $0.06 (TOU billing), Dec-to-date 393Wh/mi = 91 eMPG. Lifetime 311kWh = 115 eMPG (at current gas price)

    The only problem with your calc (that I build into mine) is charge efficiency.

    When you buy a gallon of gas you (typically) get a gallon of gas that can be used for propulsion/hvac/etc...but some of the kWh you buy are lost through charge efficiency.

    I adjust for that (or just use total kWh charged instead of Wh/mi driven).
     
    • Informative x 1
  8. wesley888

    wesley888 Member

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    Ah, good point!

    And you got some crazy cheap electricity there!!!
     
  9. thefortunes

    thefortunes Member

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    If you have the option of TOU billing, look into it.

    To break even we need to have 50% of our usage off-peak vs peak. Since we went on the plan at our current home we are closer to 85% off-peak. We both drive electric (and charge off-peak), and moved pool pump, dishwasher, clothes washing/drying to off-peak.
     
    • Like x 1
  10. Dcr26

    Dcr26 Member

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    On my drive to vegas yesterday I was averaging over 500 wh/mile and it cost me zero using super chargers :)
     
    • Like x 2
  11. Yinn

    Yinn Member

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    I'm bad at math, so I use the "Compare Side by Side" tool on FuelEconomy.gov - The official U.S. government source for fuel economy information.
    (my wife also glazes over when I talk about cost/mile)

    There's a personalize button that let's you adjust for fuel price, electricity price, as well as your driving style. It's been pretty good for me so far. It's been spot on for us.

    Diesel: $2.29
    87 Octane: $2.49
    93 Octane: $2.99
    Electricity: $0.169
    with 40% of my driving in City @ 15,000 miles/year.

    Using a MS 60D, a Jaguar XF 20d AWD (diesel), Cadillac CTS AWD (87 Octane), and an Audi A7 Quatro (93 Octane) for comparison.

    So when my wife and I have this discussion, we say our annual fuel cost is only $150 cheaper than the Jaguar. $1000 cheaper than the A7. Over a 8 year planned ownership, that's $8,000 saved on the Audi. It's not as precise, but hope it helps.
     
  12. HankLloydRight

    HankLloydRight Fluxing

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    I did it a bit differently. I calculated an equivalent $/gallon to drive the same distance compared to my ICE car which gets 20mpg. Back when gas was between $3 and $4/gallon, the number I came up with for the Model S was 37cents/"e-gallon". It probably has gone up since gas prices have declined, but that's the general range.
     
  13. Boourns

    Boourns Member

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    When I was comparing cars I compared the cost of fuel/electricity per week. I did it that way so I could roll in this number to the monthly payment to get an overall comparison of the cost of each vehicle to own.

    My formula for ICE cars was:
    H3 is the mpg of the car, 265 is miles driven per week, and 2.75 and 2 were the cost of premium and regular gas at the time.

    For the Tesla my formula was:
    That's again driving 265 miles per week at 330wH/mile with my summertime electric rate. This also does not account for charge efficiency.

    I am definitely not a math guy, so I'm sure there are better ways to do it.
     
  14. CmdrThor

    CmdrThor Active Member

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    The easiest way to compare apples to apples is calculate the $ / mile for both vehicles. Then you can multiply by miles to get your cost for any distance. For me:

    365 Wh/mi * 1.1 (charging inefficiency) = 401.5 Wh/mi = 0.4015 kWh/mi * 0.12 $ / kWh = $0.048 / mi

    A similar sized SUV would probably get around 20 mpg, average cost of gas in my city right now is about $2.20.

    $2.20 $ / gallon / 20 mi / gallon = $0.11 $ / mi

    The cost of electricity is a little less than half of what it would cost to fuel a gas car for me.
     
    • Helpful x 1
  15. wesley888

    wesley888 Member

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    Mine is $0.0864 / mile. With the 1.1x charging inefficiency, that's $0.095 / mi. Literally twice as much as yours. LOL
     
  16. Amp Dup

    Amp Dup Member

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    Just did my first calculation of fuel cost for the Model X. Whew! Electricity is expensive here in Southern Cal! Tesla uses an "average" of $0.12 per kWh in estimating savings. My cost in Tier 2 is $0.23/kWh. So, it cost me $0.105 per mile. My Honda Pilot, in similar driving for all of 2016 was $0.187 per mile. (regular gas)
    I'm sorry, but if I get into Tier 3 - $0.29/kWh - I'm heading for the Supercharger.
     
  17. kort677

    kort677 Active Member

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    I figure that the cost is about .25 cents to the dollar, my electricity is .11 cents per kwhr
     
  18. mblakele

    mblakele radial cross member

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    Most EV owners should probably be on an EV plan, where one is available. If you're in SCE territory, try Electric Vehicle Rates | Electric Vehicles | Your Home | Home - SCE — otherwise check with your electricity provider. It can be a pain to get switched over to an EV plan, but it's worth it. The PG&E rate tool tells me I'm saving hundreds annually vs the cheapest tiered rate.
     
    • Helpful x 1
  19. Amp Dup

    Amp Dup Member

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    I have looked into it some but I want to wait and see what kind of pattern develops. The car is for "pleasure" only, not used for commuting, so I'll have to see if the electric cost is significant. Do you have a separate meter on your charging circuit?
     
  20. No2DinosaurFuel

    No2DinosaurFuel Active Member

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    To all that is using the $0.12 per kWh. I recommend to go back and look at your electric bill to confirm.

    Yes, here in CA electricity is much more expensive. More so than most would think. In my opinion the rate charged at the supercharging stations is very reasonable because it does include taxes and fees.

    Most people here don't factor in the distribution charge. Here in So Cal, it is double your rate. So yes my per kWh is $0.21 for the lower tiers, but because of distribution cost this effectively becomes $0.42 per kWh. Distribution cost is calculated base on how much electricity you use. So it scales nicely in the power companies' favor.

    So if the supercharging stations charges $0.20 for each kWh without fees this is actually still cheaper than charging at home.
     

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