How Much Does it Cost to Charge?

Discussion in 'Prime Plug-in Charging' started by Tideland Prius, Jul 20, 2018.

  1. Tideland Prius

    Tideland Prius Moderator of the North
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    MPGe Le/100km kWh/100 miles kWh/100km
    1 133 1.8 25.34 16.02


    Gasoline/Petrol
    MPG L/100km kWh/100 miles kWh/100km
    1 54 4.4 62.41 39.16


    Assuming:

    EPA all-electric range (AER): 25 miles or 40 kilometres
    Rated fuel tank size: 11.3 gallons or 43 litres
    When the low fuel light comes on: 9.2 gallons or 35 litres
    Actual kWh of battery charge from "normal"* hybrid battery SOC to full charge: ~5.5kWh
    Wall outlet readout of kWh of battery charge from "normal"* hybrid battery SOC to full charge: ~6.3kWh
    *Normal being 6 bars out of 8 for Gen 1/2/3 Prius drivers or about 3/4 of the hybrid portion of the battery indicated on the onboard display.

    The EPA uses 33.7kWh per gallon of gasoline for their conversions (8.9kWh per litre of petrol)

    Therefore, if you want to calculate your cost, let

    A = electricity cost in dollars per kWh
    B = Gasoline cost in dollars per gallon
    C = Petrol cost in dollars per litre
    $ = Cost

    Use the following formulas:

    1. For cost of electricity per EPA charge

    $ = A*25.34/4 (for 25 miles), $ = A*16.02/(100/40) [for 40km]

    2. For cost of electricity per EPA charge per mile/kilometre

    $ = A*25.34/100 (in miles), $ = A*16.02/100 (in kilometres)

    3. For cost of gasoline per full 11.3 gal/43 litre tank

    $ = B*11.3 (for gallons), $ = C*43 (for litres)

    4. For cost of gasoline per real life tank (i.e. refuel at the low fuel light)

    $ = B*9.2 (for gallons), $ = C*35 (for litres)

    5. For cost of gasoline per mile/kilometre

    $ = 1/54*B (for dollars per mile), $ = C*4.4/100


    Example:

    A = $0.1/kWh
    B = $2.499/gal

    Therefore,

    1 = $0.634 (or 63.4 cents) per 25 mile charge
    2 = $0.025 (or 2.5 cents) per mile
    3 = $28.24 per full tank of gas
    4 = $22.99 per tank of gas if you refuelled at the low fuel light
    5 = $0.046 (4.6 cents) per mile


    At 10 cents per kWh and $2.499/gal gas, you're saving almost 50% by using electricity. (46% to be exact).

    If you travel 500 miles a month:

    And you used electricity for all of those 500 miles, it would cost you $12.68.
    And you only drove in hybrid (HV) mode and never charged, it would cost you $23.00
     
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  2. bisco

    bisco cookie crumbler

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    that's it!(y)
     
  3. Estew808

    Estew808 New Member

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    This a great post. Thank you! :)

    I picked up my car yesterday. I sold a Hemi powered Chrysler to pay for it... :eek:
    I haven't found all the free charging spots in my community, but for fun, I tried the "Charge-Point" system at my office. They charge what amounts to $0.36 / kWh for Level II charging. That is not a terribly attractive option. :whistle:

    Thanks again for your post!
     
  4. ziggy29

    ziggy29 Junior Member

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    Yep. That equates to roughly 9 cents per mile under EV power. At 50 MPG in HV mode, gas would have to cost more than $4.50 a gallon for this to make purely financial sense to charge up.
     
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  5. triggerhappy007

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    Did you know you get $100 to use at ChargePoint when you buy a new prime? Just put your VIN for the promo code when you sign up. At least you can get some free charging for a while.
     
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  6. ziggy29

    ziggy29 Junior Member

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    Pretty sure this was only for the 2017 models.
     
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  7. triggerhappy007

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    You are right, I didn't even see the year because I was on mobile.
     
  8. Estew808

    Estew808 New Member

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    They gave me $10, but I didn't put in my VIN. $100 is a nice promo! haha

     
  9. eric4214

    eric4214 Junior Member

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    The $100 Gift Card only comes with / came with the 2017 Prius Plug-In/Prime. It is not available for new models later than 2017.
     
  10. DonJ

    DonJ New Member

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    Your note states that a full 25-mile charge is achieved with 6.3 kW-h input. But my Prime has a 8.8 kW-h battery.

    In my calculations I use 8.8 kW-h. Is this wrong, because the 8.8 kW-h battery is never fully drained?

    Also, can you clarify where 25.34 comes from:

    $ = A*25.34/4 (for 25 miles), $ = A*16.02/(100/40) [for 40km]

    Also, is it correct to think of the Prius Prime as a Prius with a much larger traction battery? Or is the extended EV range achieved in another manner?

    Thanks,
    Don
     
    #10 DonJ, Jan 21, 2019
    Last edited by a moderator: Jan 21, 2019
  11. Tideland Prius

    Tideland Prius Moderator of the North
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    Correct. 8.8kWh is the total capacity of the battery but Toyota does not use the entire range. The actual capacity used for the EV portion is approximately 5.5kWh but due to losses to heat when you charge, you will see closer to 6.1-6.3kWh on a meter when you fully charge the car and that's number we use for cost since that is what you will be charged by your utility company (6.1-6.3kWh).

    25.34 is the kWh/100 miles.... the "fuel" consumption. (like.. gallons per 100 miles or litre per 100 km)


    Yes and no. Yes in the sense that once you exhaust the 25 mile range, it reverts to hybrid mode so it's like a Prius with extra capacity (great for going down a mountain or coming down from a ski hill!).

    The extended range is done via external charging but you can charge with the engine if you wish. Press and hold the HV/EV button to enter CHG mode. It's best to do it between 35-45mph (so country roads or flat highways) for best fuel efficiency vs. EV miles gained. You can, of course, do it at any speed if you wish to do so.
     
  12. Salamander_King

    Salamander_King Senior Member

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    I have seen in many threads here regarding PRIME charging mentioning average use of electricity for full charge is 6.1-6.3kWh at wall. I think this number is true for L2 EVSE. However, I have been using Kill-a-watt meter almost two years now and recording my at wall charge by OEM L1 EVSE each time. For zero EV range to full charge, at wall reading has been always 6.5-6.8kWh. This value has been very consistent. Is my Kill-a-watt meter off or is this normal efficiency difference between L2 and L1 EVSE?


    IMG_20190313_055527.jpg
     
  13. CraigM

    CraigM Active Member

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    The way I look at it is that your Kill-a-watt is reading the battery PLUS the current used by the EVSE itself.
     
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  14. Marine Ray

    Marine Ray Active Member

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    Home charging rules. I pay 5 cents/KWH here in Northern Nevada utilizing our power company's Time of Use program. Works out to about 1 cent/mile.
     
  15. Marine Ray

    Marine Ray Active Member

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    Why not make number 5 - .0185 x B
     
  16. Salamander_King

    Salamander_King Senior Member

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    That might be the case. If true, then even with L2 EVSE there should be some electricity used by it if measured at the wall. If I understand it correctly, most of the reported L2 EVSE electricity is by EVSE itself. So it is not really measured at "the wall" value.
     
  17. Tideland Prius

    Tideland Prius Moderator of the North
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    The most I’ve seen from a public ChargePoint site the one time I charged to full from empty was 6.45kWh.

    I’m not sure what the difference is. We’ll need more data points - more people using kill-a-watt to report their findings.

    Cause I wanted it to be easy to follow. Someone reading it can see where I got the “54” from. Or “I’m showing my work”
     
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  18. CraigM

    CraigM Active Member

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    An interesting test would be picking up the EVSE brick in your hands just before your car obtains a full charge. I’d bet the brick would be warm to the touch indicating some power wasted as heat.
     
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  19. Salamander_King

    Salamander_King Senior Member

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    Yes, it is warm. I am not disputing the fact that there is current that goes through EVSE and cord as well that waste some electricity. I am just wondering why the number I read off of a Kill-a-watt is 5-10% higher than what has been reported by others.
     
  20. KP7

    KP7 Junior Member

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    Are you seeing any difference winter vs. summer with the need to get the battery up to temp to charge?
    I'm seeing about 6.5 as well with a level 1 at 8 amp. But it's a bit of an estimate as it is from a whole house monitor (overnight with little other load--compared pre- vs post-prime).
     
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