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Using the grid as my "battery" and save Powerwalls for blackouts?

Discussion in 'Tesla Energy' started by WSE51, May 18, 2019.

  1. WSE51

    WSE51 Member

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    My electric company (LA DWP) may not be willing to give me a Time of Use meter. I have a solar meter that runs backwards when my Tesla solar panels create more power than my house is using.

    I'm thinking, why consume discharge/charge cycles on my Powerwalls when I can just send the excess power back to the grid and get full credit for it?

    If I had a TOU meter, I'd fill the PW before peak pricing starts at 1 pm, then during peak period, send any excess power to the grid for maximum value creation, and draw down on PW on cloudy days. Once off-peak starts, I can re-buy from grid at lower prices.

    But since I don't have a TOU meter, and may never be allowed to install one, doing that just chews up cycles on the PW. There must eventually be degradation of the PW with constant charging and discharging.

    Shouldn't I just set the PW to 100% for use during periodic blackouts, and use the grid as a virtual battery? Tesla told me that unlike their battery packs in their cars, it is not a problem to keep Powerwalls at 100% charge level.
     
  2. Pale_Rider

    Pale_Rider Member

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    About to have PWs installed and I’ve got full-credit net metering. I expect to use them the way you describe above as well.
     
    • Like x 1
  3. RoBoRaT

    RoBoRaT Zero Farts Given!

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    One short answer to your question of why cycle the Powerwall, for me at least, is to meet the requirement for receiving SGIP.
    It is required to "cycle" the battery - if I am not mistaken is 52 cycles in a year, mentioned in Tesla.com:

    Powerwall Support | Tesla

    Another factor is Tesla's PW2 warranty.
    It is warrantied to hold at least 70% charge capacity by 10th year, regardless of number of cycles. I plan to work the PW - and might be best to see if it will keep up (hold at least 70% charge) before warranty runs out in 10 years. After 10 years, cost to repair/replace it is on my own dime anyway.

    IMHO.
     
  4. hmgolds

    hmgolds Member

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    The Powerwall charge/discarge efficiency is speced at 90%. So, from a pure energy standpoint, you're probably better "selling back" to the grid.

    That said, you'd probably want to exercise the discharge-charge cycle monthly to make sure everything is working ok. (Unless you absolutely trust the onboard diagnostics.)
     
  5. WSE51

    WSE51 Member

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    Location:
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    Thanks for your replies. Good idea to do monthly cycling as a test. To make it real I will cut power to entire house. After installation Tesla tested this twice on sunny days during prime sunshine and confirmed the panels charged the PW, while the PW supplied the house.

    I recall being told that it is fine to leave the PW at 100% by someone at Tesla but if anyone seen this in writing can you please post the link?

    Since Tesla installed my system I can’t apply for California rebate, they are “sold out”
     
    • Like x 1
  6. boaterva

    boaterva Supporting Member

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    Do the same net-metering here in NoVa, and got the PWs for backup only since that's the only way to use solar for emergency power. Price isn't too bad for emergency power when you get the tax credit.

    I def see from reading for the last year or so that California is a legal and credit mess (with things running out....).
     
  7. hmgolds

    hmgolds Member

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    My son has solar panels and 2 Powerwalls. In his implementation, the Powerwalls, which normally charge from solar, will automatically charge to 100% from the grid if stormy weather is forecast. Not sure how Tesla determines likelihood.
     
  8. boaterva

    boaterva Supporting Member

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    #8 boaterva, May 25, 2019
    Last edited: May 25, 2019
    Storm Watch is triggered by the weather forecast and is the only override for grid charging. Good question on what likelihood, probably ‘warning’ vs ‘watches’.

    Edit; here’s all the info.

    https://teslamotorsclub.com/tmc/threads/is-this-what-storm-watch-looks-like-for-everyone.142289/page-1

    Activates for warnings. Also, 100% on PWs is really 90% and SW overrides that and ‘overcharges’ to real 100% for backup uses. Excellent.
     
  9. WSE51

    WSE51 Member

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    Turns out that Los Angeles DWP does in fact allow TOU metering to solar customers, they just make it hard to find. If you are in LA DWP and have questions, send me a private message
     
    • Informative x 1

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