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What happens when the powerwall runs out of power?

Discussion in 'Tesla Energy' started by fresnoboy, Jan 30, 2018.

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  1. fresnoboy

    fresnoboy Member

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    Hi everyone. I'm still trying to understand the behavior of the system as I try and see if getting a set of powerwalls makes sense for me, esp if I use them instead of a generator for backup.

    In the normal self use optimization mode and backup modes, what happens if the powerwall runs out of power at night when the inverters are not on and if the grid is down?

    In the generator thread, the behavior outlined was that when it hits zero, the system shuts off and doesn't come back on until the grid power is restored. This makes sense, since the solar inverters won't turn on unless they see power, and if the powerwall is discharged, then there is no power available to signal to the inverters to turn on, even if it's really sunny outside.

    If there was a reserve value that triggered a shutdown when reached, potentially the powerwall could come back online at a time when it would be thought to be sunny to try and trigger the inverters, but the way it appears these systems are wired, the house loads would also be attempting to consume power from the powerwall, and it may not be able to support that while the inverters are coming back online.

    If the inverters and the powerwall could be disconnected from the house completely, a small reserve amount of charge would all that would be needed to kickstart the inverters, and then the house could be reconnected when the powerwall was charged to a certain point. But I don't think the gateway is wired like that, is it?

    When TOU shifting becomes available, it would seem this would be even more an issue if a power outage happened towards the end of the peak period, and the powerwall had sent most of it's energy to the grid for that day. It would switch to supporting the house's load, but if it ran out of energy, and and the grid was still out the next day, I don't see how it would restart the inverters and you would be oout of power until the grid came back.

    Can someone who actually has one of these tell me what happened if the PW shutdown during an outage? Does it get the inverters to come back online somehow the next morning?

    My apologies if I have missed something obvious.

    thanks!
    mike
     
  2. eml2

    eml2 Member

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    In 1.11.2, there is always a 2-3% reserve left in the PW, even if you set to 0% reserve in the app. i.e. there is a 2-3% discrepancy of the PW SoC between the app and the Web UI. So, when there is outage and PW is drained, it still has ~2% left. Then, the next sunny morning, power cycle PW and it should be able to turn on PV inverter.

    This was told by Tesla support. I haven't tried it myself.
     
    • Informative x 2
  3. nswfugitive

    nswfugitive Member

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    If the grid is down and solar is not being produced - and your battery runs dry everything in the house shuts down. Just like if you only had the grid and the grid goes down. Of course if you want to prolong the battery you can turn off appliances or circuit breakers on the phase your battery is attached to.
     
  4. Tam

    Tam Well-Known Member

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    That's why you don't buy just 1 powerwall for this situation. Buy MULTIPLES!
     
  5. fresnoboy

    fresnoboy Member

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    Interesting, so you have to do it manually? No way to set a timer or take input from a signal of some sort?

    Can you program in a reserve so it would shut off at 15% or 10% instead running almost all the way down?

    Can you power cycle the powerwall from the app if the network connections are still powered up via UPS of some sort?

    thx
    mike
     
  6. fresnoboy

    fresnoboy Member

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    This is always about statistics. If you have an outage during really rainy weather with little sun, or someone in house does something that burns a lot of power without realizing what's going on, you are going to still have situations where you will run out of power. More PW's reduce the odds of that happening, but you can't guarantee it will keep going without a shutdown event.
     
  7. Shygar

    Shygar Member

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    It should be easy for someone to try. Flip your main breaker then run your powerwall out while it is dark. Then see if the solar starts working the next day. As mentioned, with the unreported and built in 2-3% I would suspect there would be enough power on the powerwall even when the app reads "zero" for it to kick on the solar the next day. But I saw a vampire drain of around 1% a night so if you had a few days of no sun, you may not have enough power.
     
  8. strider

    strider Active Member

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    The PW would have no way of knowing if the solar panels had sun on them. The inverters are shut down due to having lost "the grid". You could potentially rig up something with a light sensor on your roof and some kind of a relay...

    You can set the reserve to be higher to give you more buffer.

    If the PW shut down due to hitting its reserve your house is dark. I believe you'd have to physically power cycle it.

    What's the use case of you not being home during a power outage and running the PW down overnight? If you're not home your A/C should be off and heat should be set as low as it can go. What's running at an unoccupied house to burn through that much power?
     
  9. fresnoboy

    fresnoboy Member

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    Well, first off, I travel quite a bit, and I don't want my wife having to try and figure this out if I am not home. Secondly, I am a software engineer, and have a rack of servers that burn about 2kw's on a more or less continuous basis. Some of that will power down in an extended outage, but again, it's not something I want my wife having to figure out.

    I will have a ton of solar in the new house, so production shouldn't be a problem.

    One or two PW's would not be enough for my needs, but 3-4 might work. But if one PW is rebooted, and the inverters start, do the other PW's automatically detect that and power on, or would I (or my dear wife) have to power cycle all of the?

    Generators have nice automatic transfer switches that make all this easy, but hopefully Tesla will figure things out and make it more user friendly. If the system wasn't so closed, it would be easy to wire up a solution. But such is not the case...

    thx
    mike
     

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