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Waking up a Powerwall 2 in Standby

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I have been operating my two PW2 in time-based control lately with a 20% reserve and that works well in terms of getting a full charge from the solar if there is some reasonable amount of sun in the morning, and powering the house during peak pricing in the afternoon/evening. When I anticipate the possibility of a power failure, I typically up my reserve accordingly.

About 4 this morning, however, we had an unanticipated power failure and the PW2 started powering the house with the 20% of the battery left in the reserve. (I got a message on my phone at that time saying that the PW was powering the house at 89% State of Charge??). As the geothermal system started to warm up the house shortly thereafter, the PW2s ran themselves down to 5% and shut down and my generator automatically started up. About an hour later, the PW2 started putting out power again and the generator automatically switched off allowing the PW2, now at 4% SOC, to power the house. Knowing that 4% would not last long, I manually switched to generator operation.

When the generator is powering the house, the PW2 can still “see” and charge from solar, but only if it puts out a voltage and frequency that the solar inverters can use to sync. I have seen this work in the past, but not this time. At first the Tesla app showed the PW2 in backup mode, but since it was still dark there was no solar. After a while the PW2 went into standby mode and so even after the sun came up and the solar was capable to generating power to charge the PW2, the solar inverters did not see a voltage from the PW2 with which to sync, and so the inverters stayed in wait and try again mode.

How to wake up the PW2 and get it putting out a feeler voltage to get the solar going was then the question? I tried switching operational modes several time and finally, for whatever reason the PW2 went into backup mode. Progress, I thought, but even then, the solar inverters still did not see any voltage from the PW2 with which to sync. Frustrating. Soon thereafter however, the grid came back on, the solar started up and the PW2s started charging.

Since I have seen the PW2 charging from solar in the past with the generator powering the house, I don’t know why this was different and also what is the best way to wake up the PW2 so that it starts putting out a feeler voltage to get the solar going. Perhaps it was the low, <5%, SOC?
 
Do you know what the inverters said the problem was? High frequency, low voltage, or something else? That would help pinpoint where the problem was. Most inverters have either a display or a network connection where you can get this information. It's also available in the PW API, but you'd need to query it to see what it is.
 
On my newer SB inverter that is a nice screen that shows the "grid" voltage when it is there, but it showed nothing. The log on the SB webpage I use to monitor my solar system performance said "grid failure" or "grid voltage fault" during the time when the solar was up but not able to sync.
 
I don't think the modes in the app are accurate when the Powerwall has gone off-line due to low charge. The Powerwalls are supposed to check for solar every hour, but you can get them to try immediately by toggling the switch on the Powerwall: Backup-Only | Tesla Support (look for "Powerwall at Low Charge").

"Standby" is what is shown in the app if the Powerwall is neither charging nor discharging. I think the app probably doesn't currently reflect when the Powerwalls are shut down due to low charge in the status.
 
Very interesting. Seems like there was no power at your inverter. You did say with the generator off the house had power, right? That would seem to imply the inverter was on the wrong side of the Gateway, or maybe the ATS for the generator. Definitely worth testing again to see which circuits have power when the grid is down.
 
No with the generator off, the house would not have power. See attached diagram of my setup. Actually my generator transfer switch would not let me switch back to the grid/powerwall/solar side of things when none of those sources was providing power.
PowerWall 2 with Generator.png
 
According to this information on the FAQ site, this may be necessary to restart it without grid power:

To resume Powerwall operation, turn off all lights and appliances in your home, then toggle the on/off switch located on the side of Powerwall. If, after an extended utility outage, Powerwall is depleted, then wait for the next sunny day before toggling the on/off switch.

I suspect that your PW was depleted and could not sustain the load of the house. So in that case, you need to disconnect everything except the PW and solar inverters, and then toggle the on/off switch. This should bring up the PW so it can generate the proper voltage and frequency for the inverters to start. The key is to turn of all loads so the PW can startup and get the inverters going.
 
Thanks, with the generator transfer switch in the generator position, there will be no load. When I got my first PW2, I was able to use the switch on the unit to wake it up, but in my case that means a long walk to the shed with the PW2 in it. It would be nice to bring it back up from in the house, using the app. It is good to know that switching the PW2 off and on is the official solution.