To Charge or not to charge- that is my question

Discussion in 'Prime Fuel Economy & EV Range' started by Mark Schneider, Apr 15, 2019 at 4:29 AM.

  1. Mark Schneider

    Mark Schneider Junior Member

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    I’m very happy with the Solar panels we installed on our roof last year and using that green energy to propel my Prius Prime 25 miles is awesome!

    However my wife has told me we will be receiving $0.31 / kWh for extra electricity generated and sold back which is a large number ! I’m waiting to receive an actual check in May to confirm.

    In this scenario the opportunity cost of using 6kWh to charge my Prime vs selling that electric back is about $1.86 hmm... (6*0.31)
    I realize the exact charge will vary I’ve heard 6.3kWh observed in other posts in this forum but round numbers make life easier.

    Using gasoline instead would cost less at this time. I filled up for $2.65 today but let’s use $2.80/gallon for our example. I usually get 50mpg driving 75mph most of the way to work and I’m traveling between 180—190 miles each work day round trip (hence the need for a Prius)

    So to go 25 miles I would need half a gallon in this case if I’m getting 50mpg and that would cost $1.40 ($2.80/2)

    So for the same 25 miles I could use gas for $1.40 or electric for $1.86.
    That is a $-0.46 difference

    If I charge 6 days a week that difference becomes 0.46 * 6 = $2.76 / week
    In a year I drive about 50 weeks, that difference is $138.00 / year

    That’s $420 extra spent on gasoline
    And $558 paid from the electric company for selling that solar energy instead of using it.

    I really like using EV especially at the beginning and end of my commute but that’s maybe 10% of the battery capacity I suppose I could find a happy medium ...

    But curious to get some thoughts and feedback on this particular situation I’m finding myself in
     
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  2. mr88cet

    mr88cet Senior Member

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    That’s a rather curious calculation there! You are probably getting a much-higher-than-average rate for energy sold back to your utility (or perhaps you’re not really getting that much back).

    I personally don’t, yet, have home solar, but from what I’ve heard from colleagues at work who do, Austin Energy doesn’t pay them as much for energy they supply to the grid as they pay AE for energy they receive from the grid. Of course, they pay quasi-nothing (i.e., other than the cost of the panels) for energy they use directly from their panels.

    In either case though, my question is *time of day* you charge. I’ll assume you don’t have a large battery, and that you charge after peak-solar hours, e.g., after you get home from work — say 7PM at the earliest. (You’ll probably get best battery conditioning charging right before you leave.)

    If indeed both of those assumptions are true, then you’ll be charging *from the grid* and *not* from your panels. In that case your P.Prime will be at work the entire time you’re selling energy to your utility. The situation of diverting energy to your car that could be sold to the grid, would rarely ever even come up.

    That being the case, then it’s just a question of $/mile from the grid vs. from gas. In my case, those numbers work out to around 2.5 cents/mile from the grid vs. around 4 cents per mile from gas.

    Possible minor nit in your calculations: I at least am not able to charge 6KWh into my P.Prime (more like 5.5KWh), and I’m seeing about 4.6 miles per KWh, so guessing your estimate of 25 miles per 6KWh is a little pessimistic.

    (Wow, did I understand you correctly to have 180 mile daily commute?!)
     
    #2 mr88cet, Apr 15, 2019 at 6:46 AM
    Last edited: Apr 15, 2019 at 7:01 AM
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  3. Salamander_King

    Salamander_King Senior Member

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    I think you are simplifying the calculations too much. Gas price may not stay as low. The electric company may not keep paying you the same amount for the electricity you generate. AND unless your solar panel is generating in excess of what you use in your household, you can not cash in the total amount of $0.31 / kWh. If your household uses more electricity even without charging PRIME, your potential GAIN is the difference between what you usually pay for the electricity and what you get paid for the electricity generated. What is your rate for electricity purchase?
     
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  4. Mark Schneider

    Mark Schneider Junior Member

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    Some good points. At this time we have spun our electric meter back about 700 kWh from when the system was turned on almost a year ago. A new electric meter was installed and started at 00000 We generate about 9000 kWh per year.

    I questioned my wife on the 31 cents for excess kWh generated, seemed too good to be true. I will not change my daily charging until proof in the form of a check from the utility has cleared in the bank account and used to pay another utility bill.

    Yes gas prices are definitely volatile and I certainly expect prices will rise in the future and the costs will need to be re-evaluated.

    1850CF6A-19E5-40B5-83C4-2A43920F29E4.jpeg
     
  5. Raytheeagle

    Raytheeagle Senior Member

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    I can tell you out here in the Bay Area that PG&E pays $0.04 per kWh sent back to the grid at true up time:cool:.

    We are going to be slightly positive at true up, but now that we have a Prime I will be charging at home, I’ll need a couple more panels ;).

    That might be the rate they would charge if you used in excess rather than sold in excess. I believe that’s close to what PG&E charges out here if we didn’t size the array correctly and they supply us power(y).
     
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  6. mr88cet

    mr88cet Senior Member

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    Again, I think the main question is time-of-day: If your usage of a grid-tied home-solar system is typical, your panels will be generating next to nothing *at the particular time of day* when you’ll be charging your P.Prime.

    That being the case, it won’t matter now many cents per KWh the utility pays you, because at the time you’re charging, virtually all of it will all be coming from the grid anyway. So then, it’s just a question of $/mile charging from the grid vs. $/mile from gas. For me at least, that’s 40ish% cheaper from the grid. (Well, that plus all of the other advantages of EV driving — quicker gas-pedal response, lower noise, etc.)
     
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  7. John321

    John321 Junior Member

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    Mark I like the way you simplified the cost of gas vs electric. It make comparison of cost for fuel source very easy. If i understood your calculation right:
    Cost for 25 miles on gas = Price of a gallon of gas/2
    Cost for 25 miles on electric = Cost of Kwh x 6 (6.3 if someone wants to be exact?)

    While this may not be perfect and peoples individual situations are certain to vary it seems to be a quick and simple way to determine and compare cost.

    I appreciate you sharing this with us. We are determining now if we want to buy a plug in model car and want the decision to be heavily weighted on the economic factors. I have seen many complicated formulas and equations that attempt to take in variables. I believe your way is simple, straight forward and immediately gets you in the ballpark for cost comparisons.
    Understanding there may be some confusion with your cost of energy sold back and that is what people are discussing - your first electric bill or a quick call to your utility may sort that out.

    I notice that the 2019 Prime spec is 8.8 Kwh I assume the usable part of this for ev mode is 6.3 Kwh and the rest is a reserve for starting the engine etc.

    Your homes solar array looks awesome. It looks like your family is well on the way to some Energy independence from the Utility companies.
     
    #7 John321, Apr 15, 2019 at 11:12 AM
    Last edited: Apr 15, 2019 at 1:23 PM
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  8. fuzzy1

    fuzzy1 Senior Member

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    Online, I'm seeing that NJ is among the most generous states in the nation for solar incentives. They get net metering at full retail rate, not wholesale as some other states use. Though the sample rates shown here are much lower than OP lists. We'll need more information, to make sure that other charges are not being rolled into that $0.31 / kWh statement.
    For someone comparing strictly on the basis of $/mile, this 'time of day' issue matters only of they have 'time of day' metering. For flat rate metering, time of day doesn't matter.

    ===========
    In my state, I have retail net metering forever, plus a solar credit on gross production that sunsets in June of next year. Net metering doesn't pay for excess production beyond my home's use (I do currently have a small excess), and the excess defaults to the utility after a year. More reason to acquire a plug-in car ...

    Bad news / good news story: Apparently, the production credit program is closed because it has already hit the legislated cap. New installations still get net metering, but not any production payments :( because so many of us already installed solar systems :).
     
    #8 fuzzy1, Apr 15, 2019 at 12:59 PM
    Last edited: Apr 15, 2019 at 1:37 PM
  9. bisco

    bisco cookie crumbler

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    i'm amazed at how many plug in and solar owners aren't in it for the environment
     
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  10. bruceha_2000

    bruceha_2000 Senior Member

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    :eek:
    SIX hours of commute time 5 days a week!!!! Dude, get a closer job or move!

    Per the link from @fuzzy1 you are getting paid the same as you are being charged and time of day doesn't matter (though @mr88cet was smart to consider that possibility) -
    "Jersey Central Power & Light’s net metering rates are determined by multiplying the amount of net metering credits produced annually by the current retail rate, which is currently 9.4 cents/kWh. Credits are applied to future bills until used up and extra credits are credited to the customer account at the end of the year."

    You should be able so see what you are being paid and credited on your bill each month.

    BTW, 9.4/kWh is cheap, it is over $0.17 here. Plus the daily charge for the privilege of being connected to the grid and a dollar for low income customers.

    Vermont's system is like @fuzzy1's. We are credited what we are charged, credits are by month and if you haven't used a month's credit within a year, the power company gets free electricity from you. We also have a 10 year incentive (the only incentive available from the state) that pays $0.05 for every kWh generated whether the power company sees it or not. Until last year the credits could be used on any part of the bill. Newer installations are getting screwed because the credits can't be used for non kWh based charges. That means the newer people are paying a minimum of $15 a month cash to the power company no matter how big an array they installed. This is due to state legislation, not the power company.

    Consider the price of the car and your tax situation. With the federal tax credits and regional Toyota "cash back" money, you might be able to buy a new, left over, 2018 for less than a non Prime Prius with equivalent (or fewer) features. In that case your purchase is positive on both the environmental and financial metrics.
     
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  11. Roy2001

    Roy2001 Active Member

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    I cannot believe the price, it might be $0.031/kWh?

    If it is true, then you can invest on solar panels and it would pay itself in 4 years :)
     
  12. fuzzy1

    fuzzy1 Senior Member

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    I would not believe $0.031, very few places in the country have retail prices that cheap, essentially all in fully hydroelectric districts. Remember the NJ has net metering at retail rates, not wholesale.
    I'm not sure that anyplace has such good terms for significant production excess beyond what the house consumes annually.
     
  13. John321

    John321 Junior Member

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    Bruceha-2000 - thank you for your response. I in fact almost traveled recently to New York to buy a 2018 Prime but it sold as I was interacting with the Dealer. One issue with the new Prime is that the discounts you mention are indeed regional and far from our area.

    Our local Toyota Dealer has told us that distribution of the new Primes is also regional and at the time we talked to the Dealer the Southeast Region had not been granted any allocation of new Primes but hoped that would change soon. The Dealer mentioned at times they do trade allocations with different Dealers but at this time their inventory was selling well and they would not be willing to use any of their inventory for a trade in allocations.

    This is a common issue that many people experience in areas that are not in the Northeast or California. It is not unique to Toyota as we were also looking at the Kia Niro and the Dealer said the only way a person in our area could obtain a Niro Plug in was for the Dealership to locate and special order the vehicle to be shipped to the Dealership. He said our area receives no allocation of these vehicles.

    One issue plug in vehicles have is they seem to be a niche vehicle that if you live in certain areas they are not readily available and in some cases not even able to be ordered. There is even a thread started on our Forum called 'Prime sighting in the wild' that implies how rare it is to see these vehicles.
     
    #13 John321, Apr 15, 2019 at 4:10 PM
    Last edited: Apr 15, 2019 at 8:53 PM
  14. Prodigyplace

    Prodigyplace Senior Member

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    The main issue is that Toyota allocates based on vehicles of that model sold the previous year. They allocated Primes to CARB states forst so they naturally get more this year based on last year's sales.

    It is unfair to those dealers who could sell many more if they were permitted.
     
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  15. bruceha_2000

    bruceha_2000 Senior Member

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    Sad state of affairs! They probably figure all the "country folk" only want pickups, why carry cars that get great mileage. I'm on a couple of other forums and yeah, no one gives a [email protected] about MPG. I can see it if you have only one vehicle and need a PU that gets 15 MPG. But lots of people are not in that situation.

    I THINK the Primes in the wild thread was started back when the car had just come out in 2017.

    Sales based on last year's sales is a poor metric. Maybe they should consider doing some market research.
     
  16. bisco

    bisco cookie crumbler

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    or, they are too costly to toyota to try/want to sell more
     
  17. mr88cet

    mr88cet Senior Member

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    My point is that he’s most likely going to be charging at 7PM or after, and their panels aren’t going to be generating any power during that time frame. So, it doesn’t ultimately matter for how much they can sell a KWh, because during the time frame he’ll be charging, their panels won’t be producing any power to sell.
     
  18. fuzzy1

    fuzzy1 Senior Member

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    Without time-of-use pricing (many of us still don't have it), and with true net metering, that time shifting is irrelevant.

    Time of solar production, and time of home consumption, don't figure in to basic net metering. The only things that matter are the net- and production-meter totals at the end of the billing cycle.

    There are (or were) some net meters that were blocked from rolling backwards. For those, timing to production and use do matter. But OP doesn't have that.

    Similarly, time of use pricing bollixes this analysis.
     
  19. Prodigyplace

    Prodigyplace Senior Member

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    There are these amazing things called batteries that can save the power so it can be used later. :)
     
  20. mr88cet

    mr88cet Senior Member

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    Yes, as I mentioned, I’m assuming he has no batteries. Most grid-tied systems don’t, since avoiding batteries is usually why people grid-tie a system.

    Of course if he does have batteries, then he’ll lose 15-20 percent efficiency to charging and then discharging those batteries, compared to charging directly from the panels. Not a huge deal, but still part of “the equation.”
     
    #20 mr88cet, Apr 16, 2019 at 6:44 AM
    Last edited: Apr 16, 2019 at 7:12 AM
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