Solaredge Settings for AC coupling to Sunny Islands. California Rule 21

[abilityonline]

Looking for advise from anyone currently using solaredge HDwave inverters for Grid tied PV. I have successfully AC coupled 2 sunny islands through the critical loads panel with a manual transfer switch. My last step for battery backup in times of grid failure is to throttle my GT PV when grid is down and battery is full. Obviously a Sunny Boy would read a Sunny Island and tapper production if battery was full. But in this case I need to use California Rule 21 designed to adjust PV when 60hz grid fluctuates.

Has anyone successfully enabled rule 21 on a SolarEdge? What settings in the wattage did you use for Frequency Watt monitoring/?

 

[Ampster]

What settings in the wattage did you use for Frequency Watt monitoring/?

My Solaredge which was installed in California in 2019 already had Rule 21in firmware. The other spec that resembles Rule 21 is UL 1741SA. Do you know the specs of your inverter? It is typically one setting that specifies Rule 21 if the inverter is capable.
The important issue is whether your grid forming inverter (Sunny Island or Sunny Boy) can accomodate the capacity of your SolarEdge GT inverter. That may depend on the capacity of the batteries connected to the Sunny Island.

If you already have the Sunny Island and Sunny Boy AC coupled you will have to know if there is any capacity issue there. I suspect the issue may be whether more GT capacity can be added to the existing AC coupled arrangement, not whether the Solaredge can be programmed. That means you can always add GT capacity just that it may not work when the grid is down.

 

[abilityonline]

I have no need for more GT capacity. My system is 14kWp. Running 2 Solaredge 7600 HD wave GT inverters (plenty of excess capacity) coupled with 2 Sunny Island 6048 Hybrid Inverters. 960 AH 48v battery bank. My Solaredge are both California 21 capable. Because the Solaredge and SI can't communicate via ethernet, others have used frequency-watts monitoring to throttle down PV battery charging when grid is down to not overcharge the battery bank. The normal grid operates at 60 Hz. When there is no grid and SI is acting as Grid if battery gets full, Hz starts to creep up. Solaredge then proportionally lowers production.

My question is has anyone coupled Solaredge to Sunny Island SMA, and if so what Frequency Watt settings did you set the Solaredge inverters to?

 

[Ampster]

My question is has anyone coupled Solaredge to Sunny Island SMA, and if so what Frequency Watt settings did you set the Solaredge inverters to?

I tried to answer that question in my earlier post, when I described the issue as whether the Sunny Island can change the frequency not whether the Solaredge can respond.

You probably already know this, but for the benefit of subsequent readers, essentially UL1741SA (similar to CA Rule 21) is a configuration not a setting. That configuration takes care of the specific frequency/Watt relationship in which the Solaredge will response to the frequency changes by the grid forming inverter (in your case the Sunny Island). There are no detailed settings to worry about on the Solaredge. I have not AC coupled an SMA Sunny Island so my answer is only responding to the Solaredge part of the question. From reading posts by @Hedges , the issue may be whether the Sunny Island can AC couple with any CA Rule 21 inverter. The specific issue is whether the Sunny Island will change frequency in the manner that CA Rule 21 specifies so that the Solaredge can respond appropriately. Clearly the Sunny Island and Sunny Boy inverters work well together, but I have not seen post in which either of them has successfully AC coupled with other CA Rule 21 compliant GT inverters.

I have successfully AC coupled both a Solaredge and IQ7 micros to a Solaredge and no configuration of the Solaredge was necessary beyond confirming that it was CA Rule 21 compliant. You have already confirmed that the Solaredge inverters are CA Rule 21 compliant so there is nothing more needed on that side of the AC coupling arrangement.

As Hedges has explained in other posts, CA Rule 21 does not define how the grid forming inverter will control an AC coupled GT inverter. Each grid forming inverter has its own algorithm which it uses to AC couple, based on battery capacity and other factors. Those factors determine how and when it will change frequency when batteries are full or load drops. I hope that clarifies the issue for you. Have you tried to AC couple them and what happens when the grid is down and the load drops and/or the batteries are full?

 

[abilityonline]

I have ac coupled the Solaredges with the Sunny Islands in a critical loads panel. I still need to change the Solaredge settings to California 21. Unfortunately you need installer rights to have access to those settings, So I'm working on that right now. Once I have California 21 enabled, I'll run a test by disconnecting from the grid in full sun to see how it goes.

What would be sign of first trouble? The Sunny Islands would keep recycling/restarting every 5 minutes if the solaredges aren't throttling down the PV output. Does that sound right?

 

[Ampster]

I have ac coupled the Solaredges with the Sunny Islands in a critical loads panel. I still need to change the Solaredge settings to California 21. Unfortunately you need installer rights to have access to those settings, So I'm working on that right now. Once I have California 21 enabled, I'll run a test by disconnecting from the grid in full sun to see how it goes.

When the grid is up the Solaredge is just passing through its output which goes to the loads, the batteries and then the grid. They are electrically coupled but since the energy is passing through to the grid there is no algorithm activated on the grid forming inverter because it has the grid frequency as a reference..When you disconnect from the grid the Sunny Islands will provide the frequency reference and as a reference point you should note the output of the solaredge inverters, the SOC of the batteries and the loads including if the batteries are charging. That will give you a baseline to measure the changes in output if any as loads change or solar output increases or decreases.

I thought the Solaredge inverters came with CA Rule 21 configured automatically, but if the installation is not in California maybe that is not the case? What state are you in? Hopefully if they are not Rule 21, you can get your installer to change that or give you Admin access.

What would be sign of first trouble? The Sunny Islands would keep recycling/restarting every 5 minutes if the solaredges aren't throttling down the PV output. Does that sound right?

If the Solaredge inverters are passing energy through to the grid you should not see any trouble. You do have a lot of PV capacity and I do not know how that compares to the limit that the Sunny Islands can control. When you disconnect the grid if the output of the Solaredge inverters is too much the Sunny Island will ramp up frequency and you should see the Solaredge inverters ramp down their output. This may take time and there may be a spike in battery voltage. . It all depends on the SOC of the batteries and the loads. The best diagnostic plan would be to drop the grid when the SOC is below 100 percent and the batteries are charging and there is a good load. Then observe what happens when you decrease the load and/or batteries taper the charge.

 

[Ampster]

I just saw some posts on a thread that discusses some of the issue that have been encountered. Here:
Post in thread 'Sunny Boy frequency-shift regulation of power output - which models work per spec?' https://diysolarforum.com/threads/s...t-which-models-work-per-spec.6004/post-505932

 

[Hedges]

With grid disconnected, Sunny Island will ramp up frequency until power production from GT PV drops to desired level. I saw it go as high as 64 Hz or so when GT PV didn't curtail output.
Rule-21, UL-1741-SA, or whatever should work so long as "frequency-watts" is implemented. That may be an optional item to select (earlier implementations were supposed to remain on-line at full power for 299 seconds, drop off if frequency remained high for 300 seconds.)

When my loads are about zero, frequency hovers near 62 Hz, which is where Sunny Boy output drops to zero. For Rule-21, I think that would be 61 Hz. I don't know whether inverter would remain connected with zero watt output at 61.1 Hz, or disconnect. Possibly zero load would flirt with disconnction.

Default Sunny Island configuration will also go down to 59 Hz to get mechanical clocks & timers back on track. Again, possible 58.9 vs. 59.1 Hz would make a difference in knocking inverter offline. You can configure SI to not make those low-frequency excursions.

2x SI (12kW continuous output) can manage up to 24kW GT PV if never grid connected. But it can't suck that much power down to battery. Around 12kW or 14kW, it could handle 100% load dump and put the power into battery while shifting frequency over a few seconds, but only if battery accepts the current. (100A continuous per SI, 140A peak.)

If you have 14kW, that slightly exceeds 13.4kW max allowed on-grid, 240V x 56A relay. Your results may vary with line voltage.
If you put one 7kW (7.6kW?) Solar Edge on protected loads panel downstream of SI, and one Solar Edge on main panel not downstream of SI, that would avoid overloading the relays.
If you put an interlocked backfed breaker on main loads panel, then you could connect both Solar Edge to output of SI, only when not connected to grid. No issue with wattage or relay max current in that case.

I have ac coupled the Solaredges with the Sunny Islands in a critical loads panel. I still need to change the Solaredge settings to California 21. Unfortunately you need installer rights to have access to those settings, So I'm working on that right now. Once I have California 21 enabled, I'll run a test by disconnecting from the grid in full sun to see how it goes.

What would be sign of first trouble? The Sunny Islands would keep recycling/restarting every 5 minutes if the solaredges aren't throttling down the PV output. Does that sound right?

Sunny Island will keep running. It will raise frequency possibly knocking Solar Edge offline for 5 minutes (depending on how Rule-21 works.) Battery will cycle as PV produces, then doesn't.

Do you have a meter that reads Hz? My Sunny Boys only display that when out of range.

 

[abilityonline]

I have installed two switches between each solar edge inverter and the main service panel. The switch reroutes power to/from main service panel to critical loads panel. I can direct one, both or neither solaredge to the main service panel by flipping the switch or conversely switch one or both to the critical loads panel. Thus I could have one solaredge feeding/receiving from the critical loads panel and one feeding/receiving from the main grid service panel.

My panel configuration is 13.92kwp but the panels face east, south and west. So I'm never at full power.

 

[Ampster]

I have installed two switches between each solar edge inverter and the main service panel.

That would be a useful tool for diagnostics if the Solaredge inverters get knocked off line too frequently. Although if I read @Hedges response correctly, the Sunny Island should be able to handle that much power. I thought about doing the same because I thought I was approaching the limit of the Skybox. It turns out it is the AC output which matters, not the DC capacity. With your array orientations you also have some margin.
Let us know how it goes.