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Powerwall best practices with net metering

Hi, I am looking for input to optimize my Powerwall settings for maximum longevity of the Powerwalls. I am in S. Florida, and I have a 10.54 kW system with 2 Powerwalls. My 10.54 kW system should offset around 70-75% of my energy needs. My electric utility (FPL) has a net metering agreement that provides direct energy credit offsets for power sent back to the grid. With the above in mind, is there any benefit to use the Powerwalls to self power the home on a daily basis? It seems to me that my electric bill would not change at all, and the more I cycle the Powerwalls the more I will wear the batteries. Since the primary purpose of the Powerwalls for me is storm backup, what is the best setting for preserving the Powerwalls?

Comments

  • In your case, perhaps backup only mode is best. In this mode, it will only be used for power failures.

    You should confirm that your net metering doesn't have off-peak and peak rates. If so, the strategy changes where you want to charge up the PWs via solar, and discharge during the peak time. Self-powered or Advanced can do that.

    Ignoring the PWs, the net metering with different peak rates means you get credit at a low rate from solar, but get charged at the peak rate if you're using the grid at night. That's why most of us use a feature like the Advanced "Cost Savings" and set the peak rate times so it knows how to allocate the power.

    The PWs use batteries that are designed for many charge/discharge cycles, so I wouldn't be that worried about longevity.
  • Will FPL let you install powerwalls without solar and let you charge them from the grid at night using lower Time of Day charging rates and then power your house with the powerwall during peak hours?
  • FPL typically doesn’t have demand or peak rates for residential accounts. Check your bill to be sure but it is unlikely. In S. Fl, using Powerwall is only good for reducing your overall grid usage and as power back up.
  • FPL does not have peak and non peak rates in my area. According to their website, "excess energy...is subtracted from the customer's monthly usage before they are billed." It appears that it is simply a Kwh subtraction.
  • The PW warranty specifies unlimited charge-discharge cycles during the warranty period, as long as the PW is charged solely from solar PV.

    I recommend changing the PW settings to something other than "Backup Only" for a few cycles occasionally, to make sure they're functioning properly. I'd also recommend dropping the grid occasionally with the main e-panel disconnect, to make certain everything works properly to backup the house.
  • Someone else pointed out in another thread that a powerwall is 90% efficient (i.e. you get 90% of the electricity you use to charge it). Net metering is 100% efficient. In the absence of time of use differences you'll do better using the "backup only" setting. [This is what I'm doing with my powerwall.]
  • One of the conditions for accepting one of the old SGIP grants is to use PW energy for a specified number of hours during peak time in a year. I made the choice to accept the SGIP grant (~$6k) and deal with the round-trip losses.

    $6k is a *lot* of round trips, at ~1kWHr (loss) per daily "trip", in my case.
  • Thanks for all of the input!
  • Bump
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