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Winter energy use for my Model S in Boston area

Discussion in 'New England' started by David29, Apr 7, 2018.

  1. David29

    David29 Supporting Member

    Joined:
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    Messages:
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    Location:
    DEDHAM, MA
    This winter, I tried to track my car’s energy use, to quantify just how much more energy the car uses in winter. We live in the Boston area, so it gets reasonably cold here, but not nearly as cold as in the upper Midwest or Canada.

    I started tracking my energy use in November. Meteorologists seem to consider winter as being December, January and February. But we had a fairly mild February and March was quite cold, so my statistics are based upon the four months of December – March.

    As background, I am retired, so I have no daily commute and consequently my mileage is relatively low in the winter. Also, I do a lot of short trips, so that tends to reduce efficiency and increase energy use. My car is parked outdoors, so I tend to use preheating a great deal.

    Key results:

    • Over the four months, the car traveled 3230 miles and reported that it used 1234.9 kWh.

    • The average energy use per mile (as reported by the car) was 382.3 Wh/mile. The rate varied from 358.4 in March to 408.7 in January.

    o This contrasts to my 2-year average of 323 Wh/mile.​

    • Average temperatures for the month varied from 29F in January to 38F in February.
    • Over the 4 months, I was billed for 1909 kWh by the utility, 55% more energy than the car reported using. (The car reports only the energy used from the battery, so energy used for preheating is not included while the car is plugged in.)
    • The excess energy reported by the utility was probably because of:

    o Preheating the car – probably the main reason for the excess.

    o Energy losses in the AC to DC conversion process, and some losses in the electrical system itself. (I have seen estimates that these losses could be as much as 10% of the energy used.)​

    • Using the local price for gas and the cost of the purchased electricity, the cost/mile for the power was equivalent to the cost of approximately 23.6 miles/gallon over the period, with variations of 20.1-26.7 mpg over the four months.

    Although the total energy use (energy bought from the utility) is quite high, I was pleasantly surprised that the energy consumption reported by the car was not higher. Sometimes I see energy use displayed in the energy app in the 400-600 Wh/mile range, but that is for short periods. These data more accurately show what the car uses overall.

    I was, however, startled by how much more energy I purchased than what the car reportedly used. I plan to track this through the warmer months as well, and hope to see a big drop in how much energy is used beyond what the car reports.

    See the attachment for more detail.
     

    Attached Files:

    • Like x 1
  2. Warbird

    Warbird Member

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    Oct 6, 2017
    Messages:
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    Location:
    Boston
    Nice! Might you post your spreadsheet? I'd like to see how the Excess formula works. Are you aware of the TexLab app that while more than tracking trips in detail, provides a breakdown of energy usage, including Phantom Drain (energy used while parked).
     
  3. cmaster

    cmaster Member

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    Location:
    United States
    This is what I had experienced in NH. I know many members in this forum think that driving a Tesla in subzero weather (this past January 2018 cold spout for several weeks) costs less than a gas car. I'm thinking to myself after hearing their defense, "Did they check their utility bill?"

    For the month of January, I spent about 200$ in energy (cost of charging the car, preheating, etc...) vs $40 for my Honda Civic.
     
    • Informative x 1
  4. David29

    David29 Supporting Member

    Joined:
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    DEDHAM, MA
    I did post the spreadsheet above. But the upload process did not "see" my xlsx files, so I assumed they were not allowed. Did I make a mistake?
    And there really is no fancy math behind the calculation of what I called excess energy. I just subtracted the car's reported energy use for the month from what my utility meter said was used. I then calculated what percentage that was of what the car reported.
     
  5. Warbird

    Warbird Member

    Joined:
    Oct 6, 2017
    Messages:
    185
    Location:
    Boston
    The forum probably fears XLSX file macros. You might try uploading it with .TXT extension.

    How did you calculate:
    - "Cost/Mile of Purchased Power"
    - "Approx.Equivalent in MPG Regular"
     

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