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PG&E E-9A vs E-6 for Model S owners with Solar

Discussion in 'California' started by vlsidude, Apr 3, 2013.

  1. vlsidude

    vlsidude Member

    Joined:
    Mar 22, 2013
    Messages:
    14
    Location:
    California
    I am currently have an 8.4kW PV system and am on a PG&E E-6 rate. Since I took delivery of my Model S, I've been considering switching to an E-9 rate to get the very low off-peak rates for charging (from midnight to 7AM). However, because they shift the peak hours later its not clear this is a win since some of my best generating time that is peak on E-6 becomes partial peak on E-9. Also some time after dark that is partial on E-6 is peak on E-9.

    Has anyone on this forum done an analysis of this. A quick calculation suggests that unless I do *a lot* of charging off peak, I'm better off on the E-6 rate.

    Also, E-6 is clearly preferable to the new EV rate that will ultimately replace E-9.
     
  2. tritonx

    tritonx Member

    Joined:
    Nov 1, 2012
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    22
    Location:
    Redwood City, CA
    I'm in the same boat; E9 even with it's weird peak compared to the solar peak being closer to noon-3pm is cost effective compared to E6, but E6 seems better than EV. I think I'm going to go E9 and then when it disappears, hopefully I can shift to E6 instead of EV.

    I've only calculated my previous months, though, and don't know if that models the summertime accurately, since my solar only went live in Feb, and I only have a few days data on post-midnight charging with the 4.3 update.

     
  3. Elshout

    Elshout Member

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    Feb 3, 2013
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    Location:
    Novato
    I also have a PV system and looking at both rates I've decided to stay with E-6 at least for the time being. Problem with E-9 is that peak rates in the winter go to 9 PM and to midnight for partial-peak. Trying to beat PG&E is a not an easy task...sooner or later they will do their best to screw you.
     
  4. gregincal

    gregincal Active Member

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    Oct 26, 2012
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    Location:
    Santa Cruz, CA
    #4 gregincal, Apr 16, 2013
    Last edited: Apr 16, 2013
    I think you mean summer. In winter it's a total gain, because the E-9A part peak is cheaper that the E-6 off peak. Even in Summer for the hours from 9pm to midnight you are paying 10.16 cents (E9A part peak) versus 10.07 cents (E-6 off peak). The real killer is summer evenings from 7-9 pm where you are paying 31.1 cents (E9A peak) versus 17.5 cents (E6 part peak). However, I'll wager the savings for off-peak EV charging more than makes up for it as long as you drive a reasonable amount each day.

    (note that this is assuming your solar panels keep you inside baseline. I haven't investigated the higher tiers closely.)

    As an example, during those two hours we tend to use up to 2kWh, which would be an extra 30 cents per day. However, I average about 60kWh of EV charging each week, so say an average of 8 kWh per day. Since I save about 6.2 cents per kWh of charging (3.8 cents E9A off peak versus 10 cents E6 off peak) that would be a savings of about 50 cents. And how the 31 cents versus 29 cents peak charge affects you depends on how your daytime energy usage gets offset by the solar. And you can see how energy usage in the evenings and the amount of off peak charging you do makes a big difference. You just have to pick some typical days and run the numbers.
     

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