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EV calculations revisited (or v2.0)

Discussion in 'Prime Fuel Economy & EV Range' started by IABoy987, May 23, 2020.

  1. IABoy987

    IABoy987 Member

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    In another thread I had posted what I thought was my electrical costs and somehow concluded that HV was cheaper than EV modes. After a good nights sleep I realized how I needed to do the calculations.

    Variable costs:
    off peak hour cost divided by off peak kWh equaled $0.050 per kWhr.

    The fixed costs:
    (wires, meter, fuel surcharges, etc) costs divided by combined on and off peak hours, equaled $0.087 per kWhr.

    Combining these, yields $0.137 per kWhr.

    Recharging cost:
    Other posts suggests 6 hours charging to compensate for inefficiencies, therefore $0.0137 x 6hrs equaled $0.82 charging costs

    EV cost per mile $0.82 / 25 Prime mileage equaled $0.033 per EV mile
    HV cost per mile $1.95 gas / 45 gen3 Prius mileage, equaled $0.043 per HV mile

    EV-HV break point
    Multiplying the EV cost of $0.033 by 45 old gen 3 Prius mileage, equaled $1.48,
    If gas dropped below $1.48 then I believe its cheaper to always run in HV mode with engine recharging traction battery, rather than off the electrical grid, if I am making correct conclusion.

    I know that there are calculators and charts, but just wanted to see what I could come up with.
    As always your Prime calculations may vary. ;)
     
    #1 IABoy987, May 23, 2020
    Last edited: May 23, 2020
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  2. mr88cet

    mr88cet Senior Member

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    Your electric-cost numbers are pretty similar with ours. Around 13¢/KWh, including all fees. So, around 80¢ to “fill the tank,” so to speak (although our “tank” has shrunken a lot recently for some odd reason, but that’s a different topic).

    However, back when I was still able to charge 6.2ish KWh into the battery, I was getting 30ish (real) miles per charge, so it works out to about 2.5¢ per mile.

    At $2.20 per gallon (pick a number! although that’s pretty typical under normal circumstances here in Austin), that’s 4¢ per mile on hybrid, at 55MPG, so roughly 40% cheaper per mile on EV (round numbers).
     
  3. Zythryn

    Zythryn Senior Member

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    Quick question. These aren’t really fixed, are they?
    Most of those costs are probably rated as a cost/kWh delivered.
    If any truly are fixed, e.g. $5/month, those should not be included.

    Every utility handles these differently.
    Ours charges a flat fee for the meter, then rated fees for fuel surcharges, wires and such.
     
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  4. IABoy987

    IABoy987 Member

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    Yep, you are correct, they multiply the total kWhr by some standard values to get a monthly value for meter, wires, surcharges etc. I looked at several past bills and entered them in my spreadsheet. Surprisingly the EV per mile hovers around 3.3 cents average. The EV-HV (electric vs gasoline) break-point $ does vary, but always on the low side, so always better to charge off the grid.
     
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  5. Salamander_King

    Salamander_King Senior Member

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    You should expect better mpg on pure HV from PRIME (or Gen4) than what you got on Gen3. EPA reported 53mpg is easily done. Unless you drive very fast, conservative drivers should get well over 60mpg most of the time. Unfortunately, PRIME does not offer an easy way to get the HV only mpg if you drive on pure EV.
     
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  6. mr88cet

    mr88cet Senior Member

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    MPG of course depends upon what speeds your driving is at and a few other factors (e.g., tire inflation). However, broadly speaking, I concur that 60MPG or greater, is achievable (after warm-up at least), just puttering around town.

    I’ve found though, that it starts plummeting rather rapidly above 60MPH, though, due to wind resistance. At a sustained 75-80ish MPH, I only get somewhere around 48ish MPG.
     
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  7. Salamander_King

    Salamander_King Senior Member

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    Unlike TX, We don't have a highway that allows 80mph around here. On the routine trips to Boston, my average speed is around 65mph on the highway, but I don't think I have ever had below 50mpg even during winter. The only time I hit below 50mpg was when I drove less than 10 miles in a dead of winter (subzero temp) on HV. Even at this low temperature, my routine 18 miles commuting was always above 50mpg pure HV. But, as you say, there are so many other variables that affect mpg. Yeah, your mileage may vary.
     
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  8. Zythryn

    Zythryn Senior Member

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    Generally, EPA numbers are best to use for general statements. And if you use EPA numbers for one side of the equation, you should use it for both.

    That said, if the calculations are for specific use cases, personal statistics should be used where possible.
     
  9. Salamander_King

    Salamander_King Senior Member

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    Exactly. The OP was using a 25mile EPA number for EV range but using his own past experience 45mpg from Gen3. It should be compared to at least EPA 53mpg for the HV side. That being said, both 25miles EV range and 53mpg for HV are in most part minimum numbers from my own experience.
     
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  10. mr88cet

    mr88cet Senior Member

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    Good info, and yes, that largely agrees with what I’ve seen, although I personally have very limited (not entirely zero, but very limited) experience in it with true winter conditions.

    To be more specific, here’s what I’ve seen:

    At 60MPH, the engine is still able to turn of fairly routinely, probably altogether being off around 15-20% of the time, based largely upon terrain. When it is on, it’s mostly to climb a hill or overpass bridge (and a while thereafter), and it usually stays pretty quiet. As a result, I still quite often see 60MPG even at that high a speed.

    However, at 65MPH, I’ve found that the ICE far more rarely gets a chance to shut off, and starting at 70MPH, the engine is audible and can rev medium-high from time to time.

    I’ve never driven it faster than 85, but there is a stretch of tollway between South Austin and Lockhart with an 85MPH speed limit, and I have indulged that once (well, twice — once to and one back). That same tollway in my neck of the woods has an 80MPH speed limit, so 80MPH much more often.

    At 80MPH, the ICE starts revving high. At 85, I wouldn’t say that it sounds like it’s “straining,” but ... well, let’s say you‘ll have no problems hearing it!
     
    #10 mr88cet, May 24, 2020
    Last edited: May 24, 2020
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  11. fuzzy1

    fuzzy1 Senior Member

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    In my service district, the meter charge is the only true fixed cost. A fixed charge per month (actually per day, with days per billing cycle somewhat variable). All the other fees and surcharges are per-kWh, so flow directly into the variable cost column.

    Beware, your decimal point is slipping again. ;)
     
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  12. IABoy987

    IABoy987 Member

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    If that's the only thing slipping at my age, I'm doing good! :D
     
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  13. route246

    route246 Member

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    I just picked up my 2020 Prime Limited a few days ago. Loving the learning curve aspect, BTW.

    I have one question. Why are you considering your sunk costs? They are done and non-recurring. If you moved and never charged your car again would those costs still be relevant?

    Isn't the only relevant cost the recurring cost, that is incremental costs per KWh?

    We pay about $0.11/KWh where I am. I use the level 1 charger. The bulk of sunk costs are absorbed by the normal use of the house including lights, A/C, TV, computers, etc. I had to buy a 12/2 extension cord which is a sunk cost but that extension cord can be repurposed for something else if I'm not charging the Prime.

    I figure it costs less than $1.00 to charge up or about $30.00 per month maximum because I have a short commute to work (pre-COVID) and would probably not full charge more than once a day. Our electricity use is pretty high (about $150/month) because we just use a lot of electricity for entertainment, computers, appliances, etc. so adding 20% because of the Prime is not significant and that is compensated by lower gasoline consumption.

    I'm just trying to get my arms around my cost analysis. I'm not a CPA, BTW.



     
  14. IABoy987

    IABoy987 Member

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    What I was doing was capturing all the costs associated with what the true KWhr would be. I guess my analogy would be if you had a regular ICE engine car and just added up all the gasoline costs divided by the total miles driven in year, but neglecting the auto insurance, oil changes, tire rotation costs, maybe garage rental if apartment dweller etc that might double or triple or more the true cost per mile of car ownership.
    And like you, I am not a CPA and sure others might chime in, that like wise I should calculate those costs into the KWhr cost. But I was just trying to just capture what the nightly "pure" KWhr cost was ignoring other factors.

    Thanks for asking. :)
     
  15. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Speaking from an accounting perspective, I don't think you should include fixed costs in your calculations. You'll pay those costs whether you charge the Prime or not, so it's not a cost attributable to charging.

    To think of it another way: distributing the fixed costs over your kWh consumption means charging your Prime reduces the overall price per kWh for all electricity consumed. Your A/C becomes less expensive to operate, your lights, your dishwasher, and everything else electric. If you distribute the fixed costs to your kWh consumption, the savings in the form of reduced per kWh charges for other use has to be credited to the cost of charging the Prime.

    Just to make calculations, imagine you use exactly 1,000 kWh per month if you don't charge the Prime. Your bill will have $87 in fixed costs and $50 for 1,000 kWh. Your total bill ($137) divided by your total kWh usage (1,000) gives us $0.137 per kWh.

    Now suppose you introduce the Prime into the mix. Say you charge it once every day. A charge takes about 6.5 kWh x 30 days = 195 kWh. Your bill will now have $87 in fixed costs and $59.75 for 1195 kWh. Now your total bill ($146.75) divided by your total kWh usage (1195) gives us $0.123 per kWh.

    Running your 5 kW central air for an hour every day before charging the Prius used to cost $20.55 per month, but now with the Prius charging figured in it only costs $18.45 per month. That difference has to be credited to the cost of operating the Prius if you want to have a full accounting.

    The difference is $0.137 - $0.123 = $0.014. Multiply that by the 1,000 kWh not used to charge the Prime and you get $14 in savings that have to be credited to its operating cost. 195 kWh x $0.123 - $14 = $9.99. When you divide that by 195 kWh you're back at the original $0.05/kWh that you would have been if you just excluded the fixed charges.
     
    #15 PiPLosAngeles, Jun 13, 2020
    Last edited: Jun 13, 2020
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  16. jerrymildred

    jerrymildred Senior Member

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    Nailed it!!!
     
  17. Salamander_King

    Salamander_King Senior Member

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    It depends on how the "fixed costs" are defined. As pointed out by @Zythryn and answered by op @IABoy987, his "fixed cost" is not fixed but it is charged by the multiplied rate of kWh used. So it is still a variable rate. In this case, it has to be included in the calculation otherwise the true cost of charging can not be determined. My utility charges supply cost and distribution cost, supply cost is what I pay for electricity I buy from the wholesale electric company, not necessarily the utility, the distribution cost is for maintenance and services for the meter, wire, etc that goes directly to the owner of the grid infrastructure which is the utility company. Both rates are charged based on the kWh used, thus I must include both for my calculation.

     
    #17 Salamander_King, Jun 14, 2020
    Last edited: Jun 14, 2020
  18. jerrymildred

    jerrymildred Senior Member

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    Naturally. If they vary according to use, the are, by definition, not fixed.

    Here's my last bill. The three components that are based on kWh come to 8.975 cents per kWh. Then there's a fixed charge of $10.58 that I pay for the profound honor of having Duke Energy sell me electricity. I pay it whether I charge the car or not. It makes no sense to include that in the cost of charging unless charging was the only way I used electricity.

    Screen Shot 2020-06-14 at 1.10.17 PM.png
     
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  19. Salamander_King

    Salamander_King Senior Member

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    Yeah, if my total electricity bill is as low as yours, adding a $10.58 customer charge into the calculation may skew the result, but our electricity bill is usually over $200/mo, even if such fixed cost existed, adding that much onto my calculation would not change my overall /kWh rate too much.

    Since the COVID-19 lockdown, I have not been charging my car much, our electricity bill is now a record low $158/mo of which I pay Supply, Conservation Charge, Stranded Costs, Transmission, Distribution, and tax, all calculated rate per kWh used. The only fixed fee I pay is $17.90/mo for 1000kWh buyout of Green Power which subsidizes renewable energy sources. This is an optional fee I elected to pay for our average 1000kWh/mo use of electricity but is not tided to our actually used kWh. It is truly fixed at this amount. I still include this on my rate calculation since it is a part of my overall renewable energy conversion effort as PRIME is.
     
  20. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Perhaps not missed by most on this board, but just in case: If you own your home and don't have solar power yet, check refinancing rates. I was able to refinance to a rate that was so much lower than my original 3.625% loan that I received $75,000 cash out and my payments and payoff date did not change. To keep that money tax free it will be re-invested in the house in the form of solar, pool repairs, and some other capital improvements. Just thought I'd mention it since people might be able to get solar and other stuff for "free".