Does PW2 support incremental frequency shifting for supply/load management?

[wwhitney]

I haven't researched this, I thought perhaps someone already knows the answer.

We know that in off-grid mode, PW2 can raise the frequency high enough to shut off all PV production when the batteries are approaching full and PV production exceeds demand. I think I read a post recently that it can first do smaller incremental frequency increases to attempt to curtail production rather than just shut it all down. Is that the default behavior or does it require some configuration on the PW2 end? Obviously whether the PV inverters support curtailment that way is a separate question.

On the load side, if the microgrid demand exceeds the available supply (PW2 inverters plus any PV production), ultimately the PW2 will shut down. But it has some surge capacity, so it may not need to shut down immediately. Does it drop the frequency below 60 Hz (perhaps incrementally) when the required power production exceeds its continuous rating and it has to start into its surge capacity?

I recently learned that there are commercially available load shed devices that are designed to trigger solely off AC frequency and can disconnect loads when the frequency drops below 60 Hz. So I'm wondering if they might be compatible with PW2.

Cheers, Wayne

 

[RKCRLR]

I have 2 PV systems, an older string system that does not support curtailment and an Enphase system that does support curtailment. The Gateway appears to raise the frequency incrementally when the PWs are close to being fully charged. My string system appears to drop off first (doesn't take much) and then the Enphase system appears to curtail production until the PWs are fully charged and then drops off completely. But I haven't explored this much. I have noticed that solar production doesn't restart until the PW's SOC gets into the low 90% range.

The Gateway (at least mine) has a load shedding terminal. I believe it is normally closed when the grid is up and goes open when the grid goes down.

 

[gpez]

We know that in off-grid mode, PW2 can raise the frequency high enough to shut off all PV production when the batteries are approaching full and PV production exceeds demand. I think I read a post recently that it can first do smaller incremental frequency increases to attempt to curtail production rather than just shut it all down. Is that the default behavior or does it require some configuration on the PW2 end? Obviously whether the PV inverters support curtailment that way is a separate question.

If you haven't already check out this post I made a few years back: Utility outage simulation data dump

Tl;dr is that I found my Powerwall's default behavior was to scale frequency based on the Powerwall SoC and the home draw. This behavior didn't change when I ran my outage test this year (though I don't think I posted the results here...). When I enabled curtailment on my Enphase inverters all I did was apply a new grid profile to it and did not touch the Powerwall config.

On the load side, if the microgrid demand exceeds the available supply (PW2 inverters plus any PV production), ultimately the PW2 will shut down. But it has some surge capacity, so it may not need to shut down immediately. Does it drop the frequency below 60 Hz (perhaps incrementally) when the required power production exceeds its continuous rating and it has to start into its surge capacity?

Great question, I haven't tested this personally and am curious to hear if someone has. As I noted above the Powerwall does lower frequency as the home draw increases - I'm not sure if this is an artifact of the physical act of drawing more (but since the inverter isn't a spinning source I'm not sure that's the case) or something the Powerwall calculates and changes for exactly this situation.

 

[Flick75]

I have noticed that solar production doesn't restart until the PW's SOC gets into the low 90% range.

That's interesting. I experimented with this last year during some off grid ops. I saw that solar shut off around a PW SOC of 97% when the frequency raised to around 62Hz. It seemed to cycle between 96-97%. The inverters would slowly comeback up until around 97% and then production would stop again. For me it cycled consistently between 96-97%. The SE inverter operating frequency range is between 59.3-60.5Hz.

I had Tesla lower my PW shutoff frequency from the nominal 65Hz down to around 62.5Hz because I still have UPS' that don't work well above 63Hz.

 

[wwhitney]

If you haven't already check out this post I made a few years back: Utility outage simulation data dump

Thanks for the pointer and the data dump. Having SOC on the graph would be interesting.

Once the frequency returns to near 60 Hz because the SOC has dropped enough, the behavior seems clear until the very end: the frequency is 60 Hz/59.9 Hz when the PW2 is net discharging, and 60 Hz/60.1 Hz when the PW2 is net charging. Not clear to me why it briefly jumps to 60.2 Hz at the end (possibly I am reading the increments wrong, and they should be 0.05 Hz instead of 0.1 Hz the above assumes).

Repeating the test at fairly high battery discharge ( below 5 kW per PW2 with excursions above) would generate the data that would address my second question.

Cheers, Wayne

 

[RKCRLR]

That's interesting. I experimented with this last year during some off grid ops. I saw that solar shut off around a PW SOC of 97% when the frequency raised to around 62Hz. It seemed to cycle between 96-97%. The inverters would slowly comeback up until around 97% and then production would stop again. For me it cycled consistently between 96-97%. The SE inverter operating frequency range is between 59.3-60.5Hz.

I had Tesla lower my PW shutoff frequency from the nominal 65Hz down to around 62.5Hz because I still have UPS' that don't work well above 63Hz.

I haven't checked this lately. I called Tesla about it because it seemed you'd want to solar to kick in sooner than a low 90% SoC. Tesla told me this is normal depending on conditions.