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All-In Electricity Costs for Model S

Discussion in 'Model S: Battery & Charging' started by mknox, Aug 9, 2012.

  1. mknox

    mknox Well-Known Member

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    Hi,

    I've been doing some calculations on what my "fuel costs" (as measured by my home's utility meter) are going to be for Model S using Tesla's own estimate of 300 Wh/mile when it occurred to me that there would have to be losses associated with the charger, battery and so forth. In addition, there must be some sort of "standby draw" when the car is plugged in, but fully charged, and also when pre-conditioning the car for heat or cool before heading out.

    This would mean I would have to supply more kWhs through my utility meter than the car is actually delivering on the road, and my all-in electricity costs for having the car will likely be higher than 300 Wh per mile of use.

    I'm wondering if any current EV owners have actually separately-metered their EV power source (I intend to when I wire up my 14-50 outlet in the garage) and have an idea of what their actual all-in electricity use looks like.

    I suspect that Tesla's 300 Wh/mile may be a little light to begin with. Our current Chevy Volt is averaging about 330 Wh/mile when in electric mode, according to OnStar.

    The savings over gasoline looks stupendous even if I assume 350 Wh/mile, but I worry that I might be missing electricity use associated with having the car for these other, perhaps unaccounted for, factors.

    Mike
     
  2. mnx

    mnx 2013 P85

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    epa.gov says 38 kw-hrs/100 mi (and I believe that accounts for charging efficiency).

    Standby draw will be negligible compared to moving/charging the car.

    As far as preheating/cooling the car I have no idea what the usage would be there...
     
  3. Todd Burch

    Todd Burch Electron Pilot

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    I haven't done any calculations, but I suspect that (other than the efficiency losses while actually charging), the standby and other losses are incidental and, as a percentage of total use, quite small. I'd guess just 1-3% for battery temperature maintenance, preheating, and other incidental losses (modem, monitoring systems, etc.). Just a hunch though...I have no data to back that up. I think the active thermal maintenance is only used in extreme temperature ranges, which are less common over the full year of the car sitting around.

    For example, My garage reaches a maximum steady state temperature of about 99.6 deg F on our hottest days here in Virginia (about 110-115 degF). At that temperature, I don't think the active thermal management is needed on the Model S. But then again, I haven't read the manual yet...
     
  4. mknox

    mknox Well-Known Member

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    Thanks... those are good numbers for planning.

    Heating and a/c probably draw close to 1,500 watts, although would start to cycle once the car reaches set-point temperature.
     
  5. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Assuming they use a variable speed scroll compressor like the Prius, A/C usage can vary from 0 to 3200 W.
     
  6. ChrisC

    ChrisC see signature

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    I get as "bad" as 55 kWh per 100 miles in my Chevy Volt. I drive with a lead foot (and in Sport mode, a sadly unheralded feature of the car) and with climate control cranked to whatever I need. Fortunately my daily commute is well within the 35 miles nominal pure electric range, so I can use up the stored energy with wild abandon like this and nearly always still get home still under electric power.

    Just saying ... if you drive aggressively, you might want to crank up that Watts/mile number.
     
  7. mknox

    mknox Well-Known Member

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    Wow. That's about what a moderately sized house would use for central a/c! I figured 1,500 watts because that's about the wattage of a 6,000 btu 120 volt window air conditioner.

    Thanks,

    Mike
     
  8. slavi

    slavi Member

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    Sure, but the home AC would be using that continuously for hours. How long have you had the max AC on in a car? Even on the hottest day, I have to turn it down after 5 mins.
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Because it's variable speed it hardly every goes anywhere near the maximum, but that's what Prius group members have measured when they were trying to find the maximum draw. In practice, the a/c doesn't hurt mpg anywhere near the amount that running the cabin heater does as you can see from this year's log (so far 108 F has been the maximum):

    DATE__________ODO____INC_____AVG
    --- Trip to NE starts here
    01/07/12____128603____481____56.6 (4.2)
    -- 13 F here
    01/12/12____129042____438____52.7 (4.5)
    01/15/12____129420____378____50.3 (4.7)
    01/20/12____129094____481____56.2 (4.2)
    --- Trip to NE ends here
    01/31/12____130503____600____69.8 (3.4)
    02/23/12____131050____546____69.4 (3.4)
    03/07/12____131679____629____72.2 (3.3)
    03/23/12____132319____638____71.3 (3.3)
    04/12/12____132987____668____74.0 (3.2)
    05/02/12____133647____659____74.3 (3.2)
    05/18/12____134272____624____73.4 (3.2)
    --- Flat tire here
    --- High temperatures start here
    06/06/12____134907____634____74.1 (3.2)
    06/22/12____135557____650____74.2 (3.2)
    07/11/12____136210____652____74.3 (3.2)
    08/02/12____136901____690____75.8 (3.1)
    --- Trip to NE starts here
    08/03/12____137499____597____57.8 (4.1)
    08/04/12____138145____645____61.7 (3.8)
     
  10. mknox

    mknox Well-Known Member

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    I always thought that cabin heating would consume more than a/c, but on numerous occasions, Tesla reps have said heat and a/c both have about the same impact.

    Mike
     
  11. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That is likely true in the Tesla because there isn't a gas engine that has to run to provide cabin heat.
     
  12. Doug_G

    Doug_G Lead Moderator

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    Definitely not true with the Roadster - the cabin heater takes significantly more power than the A/C.

    That said, I remember hearing that the Model S has a heat pump, so heating and air conditioning may be a lot closer in power demands (except perhaps at extremely cold ambient).
     
  13. Todd Burch

    Todd Burch Electron Pilot

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    Exactly. Resistance heating will eat power for lunch. Heat pumps as used on the Model S will have more similar power draw when comparing heat vs. cold.
     
  14. agileone

    agileone CDN P#40

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    Heat pump in Model S. Really?

    Wonder how much heat these will put out by -25C.

    I know my home heat pump goes out of function and electric heating comes in, under -10C.
     
  15. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Well, Air-Source Heat Pumps | Office of Energy Efficiency says they can work below that, with equivalence to resistive heat down to -15C (5F). If(f) the heat pump in a car can be efficient to such low temperatures that'd make a big difference in northern states.
     

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