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Stupid question alert!

Discussion in 'Model S: Battery & Charging' started by Tevvy, Oct 3, 2017.

  1. Tevvy

    Tevvy Member

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    Hi all, this might be so obvious I almost feel silly asking, but can someone tell me how much electricity it uses to charge my S75D at home?

    For example, if I am almost empty of charge and I fully charge my car for 24 hours on the 240v (10amp) charger that came with the car, does it cost me 75kws? I pay 12.5p per kwh so for a full charge is that going to cost me £9.38 to fill up?

    Sorry to ask such a dumb question........
     
  2. RLC3

    RLC3 Member

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    Not a dumb question. Probably you will not run your battery below 10% regularly, and you shouldn't if you can help it. And probably you won't regularly charge to over 90%, and you probably shouldn't, if you can help it. But your entire battery capacity is 75KWh, yes. So 9.38 * 0.8 = ~ 7.5 pounds per 'fill up'.

    Note that this isn't too different from what happens with an ICE car. We don't generally run the tank empty before filling it up again.

    Enjoy your new car!
     
    • Like x 1
  3. scaesare

    scaesare Well-Known Member

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    Not dumb.

    Short answer: you have it about right.

    Long answer: There's some hidden "buffers" in the battery, so the actual usable capacity of the pack, and hence a full charge, is slightly less than 75KWh. However the charger and associated systems aren't quite 100% efficient, so there will be 5-10% waste.

    So in general count on paying for slightly more KWh's than actually get to the pack.
     
  4. Zextraterrestrial

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    there will be some extra energy used through AC-DC conversion and some losses in wiring heat etc
    I think it is less than 10% overall - there are some people around here that have logging on their power.
    & Temperature will make the biggest difference.
     
  5. Tevvy

    Tevvy Member

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    Cheers guys, so say £9 to do around 200 miles?

    The equivalent speed ICE car to mine would probably do 25 mpg, which in the UK would cost about £45 to do the same 200 miles, so it's about a fifth less in fuel costs.

    If I keep the car for 250k miles, that is 'literally' going to save me £60,000 in fuel alone?

    And that's assuming I never use the free superchargers, or free Pod Point chargers that are dotted around, and that petrol stays at the current low cost (which it won't).

    Is it my man maths, or is the most expensive car I've ever bought going to turn out to be free if I keep it for 250k miles?

    What am I missing?
     
  6. jelloslug

    jelloslug Active Member

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    My Model S costs about $30 for 1000 miles. A comparable sized car would cost about $130 for fuel.
     
  7. Rocky_H

    Rocky_H Active Member

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    Here is some of the simple way I run through this math with people. The car gets around 3 miles per kwh as a ballpark estimate. If you do about 12,000 miles per year, divide by 3. That's 4,000 kwh energy use, times the cost of your electric rate, which you said is 12.5 p per kwh. That would be 500 pounds for the whole year for charging. That's probably a lot less than you would spend on petrol for 12,000 miles in a year.
     
    • Helpful x 1
  8. Tevvy

    Tevvy Member

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    A US gallon is about 0.83 of our UK gallons (I think), so the equivalent price per gallon for us is about $6. What do you guys pay for a gallon in the US?
     
  9. RLC3

    RLC3 Member

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    Probably you aren't going to get the price of the car to zero by driving 250k miles, but it will be the MOST FUN you've ever had driving that far before!
     
  10. RLC3

    RLC3 Member

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    The imperial gallon is bigger than the US gallon, not smaller. Here in Oregon gas (petrol) is about $3.75US per gallon.
     
  11. Rocky_H

    Rocky_H Active Member

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    That varies a lot state to state because every state has their own level of gasoline taxes. In Idaho right now, we're at about $2.79 I think. Yeah, the rest of the world has more realistic prices, and the U.S. is artificially low from what it should be.
     
  12. jerry33

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

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    It has cost me less than $2,400 for 96K miles (Assumes all charging happens at home and electricity is 10 cents/kWh--actual electric rate is less). So if we use $2,400 for 100K, that's 41.6 miles for a dollar. It's actually better than that because about half the miles are trip miles which don't cost anything except the last charge at home. However, some of the SC gain it eaten up by charging inefficiencies, so the real number is closer to 55 or 60 miles for a dollar.
    Oct_1_2017_jerry.jpg
     
  13. RLC3

    RLC3 Member

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    Here you see the result of not buying gas anymore. I'm unclear on the price! It's actually about $2.75. And yeah, it's only that low because our national policies are more affected by money than common sense.
     
  14. Tevvy

    Tevvy Member

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    It just seems a no brainer to me..........I struggle to explain it to people at work, but this car will really be free (for me in the UK) after 250,000 miles. Which for me will be about 6 years.

    In reality it will probably be about 200,000 miles, given the tax incentives we enjoy currently, no servicing costs, cheaper road tax, free charging points, etc, etc).
     
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  15. RichardL

    RichardL Member

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    In the US, we can select 'Time of Use' charging rates as well - for instance in California we can select an EV rate that means we pay more during peak times and then get very cheap electricity in the middle of the night. So by starting charging at midnight (which is fine, its usually done by 2 - 3 am) it is very much cheaper.

    Of course you pay more in the afternoon, but many of us have solar, which easily offsets this on most days
     
  16. jelloslug

    jelloslug Active Member

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    In my area, low octane is about $2.50 a (US) gallon, high octane is about $2.90 a gallon, and diesel is about $2.60 a gallon.
     
  17. Tevvy

    Tevvy Member

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    Yeah so the fuel looks about double the cost in the uk to the us then. So maybe not as big an incentive for you guys but still worth it.

    We have some cheaper night time tariffs too. Called ‘economy 7’ as its typically midnight to 7am. But the daytime rate jumps up quite a lot so it probably isn’t worth it. But I can get the night time rate down to about 6p/kWh. But day jumps to 18p.

    As for solar. You need sun for this right??? Not great in the uk for this!
     
  18. jerry33

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

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    I think the real issue is that the "cost justification" makes it sound as if it's a downgrade rather than what it is: an upgrade. No one cost justifies an upgrade.
     
  19. conman

    conman Member

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    In Australia we have an electricity supplier who puts in a special meter just for your EV and charges only $1 AUD per day for unlimited charging of one vehicle. Hard to compare that to anything else, especially if you do a lot of travel each day.
     
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