Energy Products

Question. Powerwall and power outages

edited November -1 in Energy Products
If I have an PV system with integrated Powerwalls and the utility power shut off for any reason.
Is there short period of time I would be without power?
Or is it like a true U.P.S. and the power switch over is instantaneous.


  • edited March 2019
    It is instantaneous, you will not have to run around and reset your clocks after a power outage unless the power is out for longer then your battery reserves.
  • edited March 2019
    @ACDC - Thanks
  • edited March 2019
    My understanding is that it depends on the state of the Powerwall when the outage occurs. If the Powerwall was currently discharging, I would expect it to be seamless since it's already providing power. If the Powerwall is idle (not charging or discharging) or charging, it first has to detect that the grid has gone away, and then turn itself on for discharging. This is never instantaneous, it takes time. Most things in the house can probably ride through this unnoticed (you may not see your lights flicker, for example), but sensitive electronics might still brown-out so your computers and DVRs and the like might reset. So some simple UPS's (they don't need to power the load for more than a fraction of a second) may still be necessary for some things. The trick is that the Powerwall plays with the line frequency to turn off any connected Solar Inverters when it doesn't want the extra power (like when it's near fully charged), and some UPSs will see this as a bad line input and keep running from their own battery rather than switching back to the Powerwalls. Others are more tolerant to input frequency and will switch back to AC just fine.

    At least that's my understanding, I have a Powerwall but am waiting for PTO of the solar system it's connected to, so I can't test any of this myself yet.
  • edited May 2019
    I have a Powerwall system and we just had a power outage. The switch over was quick, but not instant. I had to reset the clock on my stove and my server was shut off.
  • edited May 2019
    I have a 22 panel SolarCity system with 2 Tesla Powerwalls. I have Pepco as my utility and i've had 18 events since May 2018. The switch to the Powerwalls was not noticeable for 16 of them. With one event a server went off but a clock driven by the line frequency was OK. The other was the reverse: the server was OK but the clock went off.
  • edited May 2019
    Last night notification flashed on my cell phone that Storm Watch had been activated for our Connecticut area and our Powerwall was being charged by the grid. I checked the Tesla App and indeed there was the grid charging the Powerwall. And there in Bright Yellow/Orange was Storm Watch label under the Powerwall Green Circle!!!
    Before the thunderstorm arrived the Powewall was charged up 99%.
    Fortunately just rain poured down, and we had none of the potential hail, and we did not loose power.
    Now I know how Storm Watch works!
  • edited November -1
    for me switch overs are instantaneous or close enough not to matter - had a 3 hour outage this past weekend in Watsonville, CA - no one at the house noticed the neighborhood was without power - the only reason I noticed was PG&E utility has a service to text you about outages "in your area" - when I received the PG&E text I checked the Powerwall and sure enough we were currently on battery+solar and had been for about a hour…

    the switch over depends on what "mode" you are in - if you are in "self powered mode" there is _NO_ delay because the battery is already engaged and providing power to the house - if you are in "backup only" mode there me be a sub-second cut-over as the grid goes "down" the relay's in the Powerwall gateway will take some number of milliseconds to "kick in"…in both cases my experience is the whole switch over is normally no big deal with only minor annoyances from "loss of power"
  • In our last power outage, my computer UPS completely shut down and my DirecTV reset. I was told by the company that installed it that the PW changes to line frequency to below 60Hz to shut off the inverter if the charge is above 90% on the powerwall. I'm sure it's this frequency change that is causing me problems. It would be nice if there was a way to keep the powerwall at just below 90% charge to keep this from happening.
  • bpbp
    edited July 22
    When the Tesla Gateway detects loss of grid power, there is a short period that ranges that could last up to a second or two when there isn't any power provided to the house while the Gateway shifts power to the PowerWalls and sets a power frequency.

    If the PowerWalls are full or almost full, the Gateway will set the power frequency higher than 60 Hz (which may be 62.5 or 63 Hz), which causes the solar panels to stop providing power to the system. Some devices, such as UPS or motors may have problems operating on frequencies above 60 Hz, especially 63 or higher - this can cause some UPS boxes to go offline.

    If you experience this problem, contact Tesla to lower the "solar cutoff" power frequency. They'll likely need the specific solar power inverters/microinverters you have installed, so they can set the frequency to what is required by that equipment.

    If the PowerWalls are not full (or nearly full), the power frequency will be set to 60Hz.

    Normally when grid power is lost, lights will flicker and any processor-based equipment (such as a computer or possibly a DVR) may lose power long enough to reboot when the power returns [which is why you will still want a UPS on those devices.]

    NOTE that if the PowerWalls are nearly full and the frequency is set about 60Hz to cut off the solar, once the PowerWalls drop low enough to accept solar power OR the grid power returns, there may be a long delay (5 minutes?) before the Gateway makes any changes.
  • edited July 22
    I'm not sure the 90% figure given by David is correct. This last weekend, I was showing a friend the powerwalls and flipped my main breaker to disconnect the house from the grid to show him that the AC wouldn't turn off. The house was overproducing via PV and sending extra power back to the grid. When I flipped the breaker, it began sending extra solar to the battery, immediately, which was charged to 98% at the time and in backup-only mode. When I flipped the breaker back, the house stayed off the grid for several minutes before reconnecting and during that time, it kept sending extra power to the battery. So the powerwall ended up more charged than it was before the test. So, at least in the case when you're overproducing with PV, it doesn't cut off the PV if the PW is above 90% charge. I'm sure it would have to if you were at 100% and overproducing, since there wouldn't be anywhere to put the extra power.
  • edited July 22
    @SteveWin1 - I see the same thing with my system. One of the concepts of the system is to be able to go off-grid for days. Without the grid, you should be able to charge the PWs during the day, use the power at night and return to using solar and charging the PWs again. When your daily power usage is less than the solar generation, you should be able to go indefinitely.

    Now if someone has a solar system with micro-inverters, it could work quite differently. I thought most/all Tesla systems do not use micro-inverters, but standard inverters.
  • edited July 25
    Micro inverters and powerwalls work the same way...
    Or do you mean solar only?
  • I have 24 panels and 2 powerwalls new as of Aug 20. Last night during Hurricane Sally the power went out for 10 seconds, 10 minutes and 4 hours and 50 minutes. The power did NOT change instantaneously as I expected. I had to reset my clocks and still trying to reset WiFi Alexa devices. Disappointing. I don't recall this being a problem before removing my my UPS for the router and entertainment devices. Perhaps I need to reinstall it for the short time transfer time from grid to powerwall? The powerwall was in "Storm Mode" as expected and that function worked great! Switching back to grid was not noticeable. Perhaps it was the Storm Mode that caused the delayed transfer?
  • The delay in transfer, in my experience, is if the house is actually using utility grid power when the outage happens. If it happens then, the hiccup in power to appliances is just a bit slower.

    If the house is operating on some combo of Solar/Powerwall during the day, when the outage happens, then there is not enough of a hiccup to affect appliances.

    If the Powerwall is around 96% to 97% (or higher) when you go off grid and the solar is producing more than the house is consuming, then it has nowhere to store the energy. You cannot recharge the Powerwalls to 100% when you are off grid. It always causes the inverters to do 300 seconds of a pause cycle, until you consume enough energy in the Powerwalls to drop down to 93% to 94%. At that point, after a 300 second pause cycle completes, the solar will come back online to recharge to 96-97%, then it will do the 300 second pause cycle again. That on/off cycle for the solar inverters will stop when the grid comes back online.

    That is just my experience when I was using the system off grid a lot (for two months) before Duke Energy installed the smart meter.
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