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Powerwall, Solar & Power Outage

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We had a planned grid outage that lasted most of the day and this is what happened with our setup. I was very curious to know what would happen when the PW2 was full and solar was running but the house unable to use all the power.
  • The grid outage started around 9am when the battery was about 40% charged. Solar continued to generate what it could, running the house and the excess going to PW2.
  • The PW2 was filled by about 11am. When this happened, the solar inverters were shut off completely and the house ran purely off the battery. Shown in the chart below by the sudden drop of solar production to zero.
  • This lasted for about an hour and the PW2 charge reduced to 96% supplying the house. But then the solar inverters came back fully on and proceeded to charge the battery back up to 98%. That is the brief spike in the chart below.
  • BUT this time, once the battery reached 98%, the solar inverters were not shut off completely, but instead exactly tracked the house usage. The PW2 stayed at 98%, no solar was diverted to the battery, and the solar generation showed a pulse due to our refrigerator compressor turning on and off at roughly 30 minute intervals.
  • When the grid came back on, normal operation resumed.

So there you go.

EE532159-839D-4DAC-9AF1-6ABC06F83721.jpeg
 
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Reactions: Hairyman and paulp
Thanks to the contributors here as this is an interesting discussion. I have a large array 22kWp and 20kW inverter (3 phase of course) so if the grid goes down, my inverter shuts down and the Powerwall kicks in. This fine for short outages but given the prevelence of severe storms of late, I had been thinking about ways of having solar during extended grid outages. I understand the reason for this shutdown behaviour is both a lack of a 'signal' on each phase plus the inverter can't match production to load (the latter reason is speculation).

I have 2 x PW2s but only one is allowed to backup the house - my understanding is the Gateway is single phase and you aren't allowed to have more than 15kW of inverter per phase - this would be exceeded if you add 2 x 5kW PW2s plus a third of the 20kW inverter - therefore the second PW2 is connected to a different phase but not available to the Gateway during a grid outage.

I guess a future approach might be to add a small solar array (say ~4kW) to one or more phases to stay under the 15kW limit while allowing the power to either serve the house load or charge the Powerwall (or both). As they say, 20:20 hindsight is a gift many people have and I probably would have asked for a slightly different type of system being a little more in the know now. Cheers
 
I finally had a sparky come in to rearrange our circuits. We have 3 phase power, and with the PW2 only backing up 1 phase, we needed to optimise which bits of the house are backed up in the event of a grid outage. The way it was wired was not optimal. And while he was at it, upgrade the sub-board to current electrical standards since it was 30 years old.

Once the work was done, I was keen to test the off-grid performance using the “go off grid” command on the Tesla app.

But I discovered I couldn’t really test it, because what happens is that the PW2 gateway only disconnects the phase the PW2 is on (Phase A) and not all 3 phases. So Phase B and C remained connected to the grid, which of course was still on, so absolutely nothing happened.

D’oh!
 
I finally had a sparky come in to rearrange our circuits. We have 3 phase power, and with the PW2 only backing up 1 phase, we needed to optimise which bits of the house are backed up in the event of a grid outage. The way it was wired was not optimal. And while he was at it, upgrade the sub-board to current electrical standards since it was 30 years old.

Once the work was done, I was keen to test the off-grid performance using the “go off grid” command on the Tesla app.

But I discovered I couldn’t really test it, because what happens is that the PW2 gateway only disconnects the phase the PW2 is on (Phase A) and not all 3 phases. So Phase B and C remained connected to the grid, which of course was still on, so absolutely nothing happened.

D’oh!
Did you think of turning off the main switch to the meter?
 
Did you think of turning off the main switch to the meter?

I could have done that, but that would have required walking outside 😄

I thought it was interesting to find out exactly what the “go off grid” button does on the App. It’s obvious now, but it didn't occur to me at the time that Phase B and C would not be disconnected.

I wonder if the newer gateways, which are 3-phase capable, would disconnect all phases when “go off grid” is tapped?