At what Powerwall level is gateway supposed to command solar to start generating again?

[RKCRLR]

My Gateway is inconsistent at what level it commands solar to start generating again.
I'm currently is a PSPS. Once the Powerwalls are full and solar has been commanded off, it appears my Gateway normally commands solar to start generating again when the Powerwalls are down to about 97%. I have 2 solar generating systems. One is Rule 21 compliant and the other is not. Today when the power was shutdown at a little after 3 pm (my Powerwalls were 100% full) the solar didn't start generating again until the Powerwalls were down to about 90%.

What are the specific frequency shift steps vs Powerwall charge level that the Gateway should be stepping to?

 

[BrettS]

From my experience when I was running off grid for a while the powerwalls would start shifting the frequency up as they hit 98% and then theoretically once they got to 100% they would be at whatever the max frequency was set to. (I say theoretically because my inverters turn off at 60.5Hz and the powerwalls would hit 60.5Hz before they got to 99%.)

As the powerwalls powered the house and their SOC lowered they would start to lower the frequency and by 97% the frequency would be back to normal. Keep in mind that once the frequency is in the normal range the inverters won’t restart for 5 minutes. So if your house is drawing a lot of power then even though the frequency gets back to normal at 97% it’s possible that the powerwalls could keep draining before the inverters restart. However, getting down to 90% would mean that your house was drawing a *lot* of power.

You don’t say how many powerwalls you have, but assuming you have 2 and they have 13.5kWh of usable energy that would be 27kWh for two powerwalls. Each 1% would be .27kWh, so going from 97% to 90% would be 1.89kWh. In order to use that much energy in 5 minutes your house would have to be drawing just over 22kW.

Some multimeters measure line frequency or you could use a device like a kill-a-watt to see what your line frequency is and see exactly when it returns to normal. But like I said, in my experience the frequency should be normal when the powerwalls are at 97%.

 

[RKCRLR]

I should have provided more information. I have 2 Powerwalls. My power was shut off a little after 3 pm and got down to 90% a little after 5 pm where they started charging again. Unfortunately, there wasn't much solar power at this time to provide energy.

 

[BrettS]

Unfortunately, there wasn't much solar power at this time to provide energy.

Oh, that might have been the issue. When the power is out the solar power goes to powering the house first. So if there’s not much solar power then the powerwalls won’t charge, and can even discharge if there’s so little solar power that it can’t meet the demand of the house. In an outage the powerwalls will only charge with excess solar power after the house’s demand has been met.

 

[RKCRLR]

There was no solar generation whatsoever. My house was completely running off the Powerwalls between 3 & 5 pm.

 

[BrettS]

There was no solar generation whatsoever. My house was completely running off the Powerwalls between 3 & 5 pm.

Maybe I’m misunderstanding what you’re saying. Are you saying that there was no solar generation because your inverters were turned off or because there was clouds or rain or something?

 

[gpez]

From my testing the interaction between your Powerwall and PV is more complicated than just the gateway telling the PV to turn on or off. How your system reacts is a combination of your PV and Powerwall settings as well as the current state of charge and house draw.

Your PV has multiple settings for what it considers to be acceptable grid conditions, including when the Powerwall is disconnected from the utility grid and has formed it's own microgrid. If the grid deviates from those values your PV will turn off. Your PV also has settings for how long grid conditions need to return to normal before turning back on. @BrettS mentioned that for his (and for most systems as the default) that reconnection time is 5 minutes. If the grid conditions go back out of the normal range the timer is reset. Typically for newer US inverters the range is 59.3hz minimum to 60.5hz maximum with a 5 minute reconnection time.

The Powerwall can be configured by Tesla to change the microgrid frequency as a function it's state of charge and the home draw, up to a maximum. The start, stop, slope, and maximum frequency can all be changed. Powerwalls ship with a maximum frequency of 66hz and is one of the first things new Powerwall owners ask to have changed since 66hz is way higher than the 60.5hz maximum many inverters are set for.

In my personal texting (YMMV) I found that my single Powerwall sets the microgrid frequency to 60hz at or below a SoC of ~93.4% and reaches the maximum of 61.9hz at or above ~95.9%. These are approximate levels because I noticed that when my house is drawing more power frequency of the microgrid drops slightly and frequency increase as the house draw drops. Since my PV system was set at the time* to reconnect at 60.5hz after 5 minutes I could surmise that I would have to be at or lower than 94.4% for at least that amount of time before my PV kicked back in.

Since you have two different PV systems you may see different reactions at the same time if they are not configured the exact same. I'd suggest getting a dump of what the current settings are for Fmin/Fmax and reconnect time for each then monitor your local frequency and SoC during off-grid operations.

* I have since moved to a PV configuration that scales up and down production based on the frequency rather than turning on and off, which of course makes all of this even more complicated...

 

[RKCRLR]

Maybe I’m misunderstanding what you’re saying. Are you saying that there was no solar generation because your inverters were turned off or because there was clouds or rain or something?

It was late afternoon sun, no clouds. It normally takes my PV system about 5 minutes to restart after power is re-gained.
The east facing solar generation system has Enphase IQ7 microinverters which are capable scaling production. The west facing solar generation system has an old non-rule 21 compliant string inverter that is not capable of scaling production.

Previously when the grid has gone down the solar generation had restarted when the Powerwalls had gotten down to about 97% SoC. That is why I was surprised that the solar generation didn't restart until the Powerwalls were down to about 90% SoC. They were at 100% SoC when the grid went down. It was about 2 hours before they started producing again.

There was some partial shading on the east panels but the IQ7 inverters should be able to handle that. I normally have solar generation during that time of day and there were no clouds.

 

[bob_p]

When operating off-grid, there appears to be a 5 minute delay built into the TEG when switching back to solar or grid power, in addition to turning off solar when the PowerWalls are above 97%.

 

[miimura]

When operating off-grid, there appears to be a 5 minute delay built into the TEG when switching back to solar or grid power, in addition to turning off solar when the PowerWalls are above 97%.

Solar inverters have their own timeout where the power needs to be within the allowed tolerances for something like 5 minutes. Separately, the TEG has to verify the grid is clean and phase synchronized with the Powerwalls before reconnecting to the grid. I don't think that is a specific amount of time like it is for solar inverters.

 

[gpez]

Solar inverters have their own timeout where the power needs to be within the allowed tolerances for something like 5 minutes. Separately, the TEG has to verify the grid is clean and phase synchronized with the Powerwalls before reconnecting to the grid. I don't think that is a specific amount of time like it is for solar inverters.

It is a configurable amount of time just like the inverters. The difference is if your inverters are behind your TEG you can set whatever timeout you like, the device that faces the utility is the one that needs to abide by your interconnection agreement which likely means the TEG. 5 minute reconnect is very standard.