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PowerWall Cold Start without Grid Power

Discussion in 'Tesla Energy' started by Cottonwood, Apr 7, 2018.

  1. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    In an experiment today, my PoweWall/Gateway setup would not start without Grid Power.

    Here is the sequence that I followed to do a cold restart of my system that consists of a 125A breaker on my main panel feeding a gateway connected to a backup panel and a generation panel with 9.9 kW of Solar and 2 PW2's:
    1. Switched the 0/1 switches on the PW2's from 1 to 0. The PW2's were at 99-100% charge and their green light bar stayed on.
    2. Opened the 125A breaker on the main panel.
    3. The lights on the Gateway and the PW2's stayed on.
    4. Waited about 10 minutes. PW/Gateway lights stayed on, but there was no switch to backup power; the power stayed off.
    5. Pushed the "reset" button on the Gateway and held it down for about 10 seconds. All the PW/Gateway lights went off.
    6. Waited about 5 minutes.
    7. Flipped PW2 switches to On/1. Nothing happened.
    8. Waited about 5 minutes. Nothing happened.
    9. Closed 125A breaker to feed Gateway/PW system with grid power. PW system restarted.
    Does this mean that you can't start a PW system without grid power? How do you start an off-grid system? How about an extended grid outage with bad weather and poor solar production where you shut down the PW's with some battery left, then want to restart when the sun shines again?
     
  2. evp

    evp Nerd

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    My theory is that it's following the lead of inverters without batteries -- they use grid power as their frequency reference and won't function without incoming voltage. I'd suggest putting a tiny Honda generator on the upstream side of the PowerWall and see if it would sync to that. The only issue is that it might try to push joules back into the generator if the panels manage to get the battery full.

    Does the documentation say anything to confirm or deny this?
     
  3. nwdiver

    nwdiver Well-Known Member

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    I think the Powerwall still needs a software update to work off-grid. I have a Magnum Energy that can operate AC coupled off-grid. When I've tested it off-grid parallel with my Grid-Tie inverter it's SUPER finicky. I think the lack of sufficient reactive power causes significant instability in the voltage. The grid-tie inverter worked but it didn't sound happy....
     
  4. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    The PowerWall can easily, and very solidly operate as the reference for the grid-tie, solar inverters. Here is a screenshot of my system operating off-grid in backup mode yesterday; I opened the 125A breaker feeding the Gateway and backup system for this test. The 9.9 kW DC solar array was generating 9.5 kW AC off-grid with the PW's as the reference. The 2.0 kW of load is anything but stabilizing. The vast majority of that load is switching power supplies driving LED Grow Lights, DC Pumps, and electronics. Switching power supplies are notoriously difficult loads.

    Backup Solar.PNG

    The PW system was quite adept and reliable at adjusting the purity of its AC waveform to turn the grid-tie, solar inverters on and off as the batteries in the PW's filled.

    I have not found any documentation on this off-grid subject. If anyone has info, please share.

    I know that the PW1 has been used in true off-grid applications. It was shown in a video at Our Work | Give Power Foundation after you clicked on "Congo," but that video is now gone...

    I like the theory that Tesla needs a firmware update to do a cold start off-grid. As I said, this is important for both extended backup and true off-grid applications. Let's hope that there are no significant hardware upgrades needed to add this functionality.
     
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  5. nwdiver

    nwdiver Well-Known Member

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    Ah... I think I understand now... so if you open the main breaker while it's operating it keeps the house powered but if it's off with no power you can't turn it on. Interesting. Does the grid-tie fault out when you open the main? (before turning back on). How many power walls do you have?

    The trouble I had with my Magnum Energy is it can only take ~3.6kW and as near as I could tell there wasn't anything preventing it from taking more. I tested it on an overcast day once so power would be limited but the clouds parted briefly and the system that was supposed to be limited to 60A was dumping ~90A into the batteries. I stopped the test before I discovered what would happen.
    Is your grid-tied solar designed to work with the power wall?
     
  6. jrreno

    jrreno Nothin' left to do but smile, smile, smile

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    We have a similar system with 7.5kwh of Solar and two PW2s. I am unwilling to try your experiment since I’d have to shut down the whole house. If I did so during sunshine hours I would expect our SolarEdge inverter to shut down and then restart when it detected the battery provided AC. So if I understand the solar will not start because there is no AC and neither will the battery from power off?
     
  7. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    When the grid goes down (or I open the breaker) while the Gateway and the two PW2's are running, the sequence is:
    1. Gateway Main Contactor opens, and PW2's stay off while grid-tied solar inverters shut down.
    2. A second or so later, the PW2's pick up the loads and power my backup panel. You can see this by watching lights powered by the backup panel. The Tesla PW2 system is not a UPS. Because of that I have a small UPS between the backup panel and my cable modem, router, and other network gear.
    3. After 5 minutes or so of monitoring the quality of the power, the grid-tied, solar inverters are fooled into thinking they are on the grid, and start making solar power again.
    4. If the grid-tie, solar inverters are making more power than the house is using, and the battery in the PW2's get full or close to full, the PW2's corrupt the quality of their power enough for the grid-tie, solar inverters to shut down. Once enough battery is drained, etc, the PW2's make good power again, 5 minutes or so later, the solar inverters fire up again, etc. This slow off/on solar inverter cycle continues as long as the grid power is off, there is more solar power than needed, and the PW2's batteries are full.
    5. When the grid comes back (or I close the breaker again), the Gateway watches the grid power for 5 minutes or so, matches it in frequency, phase, and Voltage, and then closes its contactor without an apparent glitch in the AC power.

    My system is 9.9 kW DC of solar and 2 PW2's. I am a big believer in Klein's Law, "If it isn't been tested, it doesn't work." That is why I am going through this backup testing of my new PW2 system.

    Yes, you are correct; the grid-tie, solar inverters will not start until they see what they believe is a good, grid-power, AC waveform, and the PW2's appear to be unwilling or unable to do a cold start without external AC power present.
     
    • Informative x 1
  8. NuShrike

    NuShrike Member

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    What use-case would this be where PWs are off, the grid goes offline, and then you need to turn on the PWs?

    It seems to be a safe assumption that the PWs have to transition from grid-tie (initialized) state, than being able to turn on anytime; especially from cold-storage (which could mean unmounted).
     
  9. evp

    evp Nerd

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    #9 evp, Apr 8, 2018
    Last edited: Apr 8, 2018
    So, the PW might power up if a small external generator were to put up a reference frequency from the grid side. It would then supply power to the house while waiting for 5 minutes to start accepting grid power. During those same 5 minutes, the solar inverter is evaluating whether it should come on line too (my inverter does the same thing). If you shut down the generator during this interval everything should be booted and happy.

    Of course, the PW should be able to boot by itself. But NuShrike's comment about randomly rebooting in the box is, I think, an important design consideration. It needs a "Yes, I really want you to launch now" button with a guard. Like the ones in the Titan missile silos.
     
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  10. jrreno

    jrreno Nothin' left to do but smile, smile, smile

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    MY PW2s kick on immediately. I have the PW2s in self-powered mode. So if I flip off the main breaker the batteries instantly take over. There is a tiny detectable flicker but not enough to impact anything in the house like clocks or computers. The Inverter shuts down and comes back online same as yours. I have Net Metering so when my PW2s are at 100% and house demand is lower than production the solar starts pushing power out to the grid.
    I completely understand the wisdom of testing all scenarios, smart move.

    IMG_0160.png
    Yellow is solar, green is battery, grey is grid.
     
  11. Ampster

    Ampster Active Member

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    As others have said, there is no need for the small generator. When the grid is down or someone turns off the main breaker the Powerwall and the grid tie inverters are isolated in their own circuit and the Powerwall provides the reference frequency.
     
  12. eml2

    eml2 Member

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    I can give you a use-case scenario. You have an extended power outage. PW is providing power to the house, and solar inverter is working properly since it sees a good reference from PW.

    It is in the middle of the night and power is still out. Your PW is down to 5% and you don't expect power comes back in the morning. However, weather forecast for the day is sunny. So, hoping to start the solar inverter in the morning, you manually shutdown PW to preserve the 5% left in it.

    Come the morning, power is still out, the sun is shining. If you turn on PW now, will it be able to power itself up and provide a good reference to solar inverter so that it will be recharged?
     
    • Informative x 2
  13. jrreno

    jrreno Nothin' left to do but smile, smile, smile

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    If you have the PW set to Self Powered mode you can select the amount of reserve in the PW. No need to manually power down the Powerwall. In addition why not just turn off whatever is consuming the power? If we were in an emergency situation I would just decide what I could live without.
     
  14. eml2

    eml2 Member

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    The reserve % works when there is grid power. When there is no grid power (power outage), I believe it will use all the power stored until it is drained.

    My scenario is about extended power outage. Assuming all the unnecessary equipment are turned off, and the PW is not fully charged when the power outage occurs. It is definitely possible that you will run out of battery power before the next morning.
     
  15. mongo

    mongo Well-Known Member

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    Minor note: the power quality stays good. What the PW does is shift the frequency higher to signal the solar inverters to reduce output. The power output vs frequency mapping is configurable on some micro inverters like Enphase. This is also what happens in the normal grid, overload-> lower frequency, overproduce-> higher frequency. Part of what the Australian Powerpack system is doing frequency/ load regulation to even out these bumps/ dips.
     
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  16. NuShrike

    NuShrike Member

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    I can see this and a more extreme situation where you just don't have enough power to restart the PW, or the PW went out and had to be somehow restarted.

    However, I'd argue instead of turning off the PW to preserve power, turn off the breakers feeding from the PW, if setting the reserve (as others have mentioned) isn't enough. Then one can avoid this extreme cold-start edge-condition.

    I wonder how other battery systems out there handle this case. I'd assume DC charged batteries don't have this issue.
     
  17. eml2

    eml2 Member

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    Good point! Maybe that is what should be done.
     
  18. mongo

    mongo Well-Known Member

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    May be an installer safety issue. Otherwise, if anyone accidentally hit the on button it would make everything live.
     
  19. NuShrike

    NuShrike Member

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    True. But we can also argue there should have a "post-install" state where the "safety" can be disabled.
     
  20. mongo

    mongo Well-Known Member

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    Definitely!
    May be a SW non-volatile setting or Dip switch.
     
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