EG4 18k PV back-feeding on GEN port

[Gubman]

Recently took possession of the 18K + 12 LL (v2) batts, running off-grid, AC coupled into an existing Enphase rollout with AC (4x10T) batteries.
18K settings follow the recommendations detailed in https://eg4electronics.com/backend/wp-content/uploads/2023/04/EG4-18KPV-12LV-Manual-2.0.2.pdf pages 25-26, wired as detailed on page 43 Diagram 4.9
In the beginning, I charged the LLs to 100% when the 18K was only connected via the GEN port. Happy with the result, I connected the 18K LOAD to the house and the following morning expecting to top off the LLs, the back-feeding was observed. The 18K back-feeds on the GEN port at about 45A on each leg, and slooooowly ramps down from there. I saw the wattage jump on the display coming out of the LL batteries - opposite of what is intended.

Has anyone observed this?
I called Signature Solar - they're scratching their heads after they connected remotely to review the settings. At this point, they, asked for a million details (pics, wiring diags, etc.) which I am compiling for them to help troubleshoot. Thought I'd throw this out at the community as well.

 

[1201]

So that others can follow along
Page 43 diagram 4.9

 

[HighTechLab]

I'm trying to understand this better - when you say backfeeding, are you referring to power coming from the 60kWh EG4-LL bank feeding into the Enphase battery bank, right?

It sounds like in the configuration you are running, the inverter is expecting Microinverters on the port that only push power into the inverter, not another ESS - so if the Enphase system is set to grid-charge, the 18kPV likely won't handle it right, because it expects ac-coupled generation, not ESS that can act as a load.

 

[Gubman]

yup - into the Enphase battery bank.
Trouble is, that I already charged the LLs previously without any back-feeding from the Enphase during the day (micros producing power) and later, evenings a bit to see what happens without sun, over several days without issue.

 

[HighTechLab]

yup - into the Enphase battery bank.
Trouble is, that I already charged the LLs previously without any back-feeding from the Enphase during the day (micros producing power) and later that evening a bit to see what happens without sun, over several days without issue.

What are the settings on the enphase batteries?

The 18kPV can't forcibly send power to the enphase system - it simply provides 240v / 60 (up to 62hz if limiting via frequency shift) power on the gen port for whichever device connected to interface with. For power to flow, it has to be pulled by the enphase system. The 18kPV can only limit imported power by frequency shifting, or entirely disconnecting the gen port. No regulation of exported power on the gen port in this configuration.

 

[HighTechLab]

I may be misunderstanding your configuration - do you have gen port setup for AC coupling / microinverters, or are you treating the Enphase batteries as if they were a backup generator (no ac coupling)?

 

[Gubman]

There's not much to set on the Enphase batts (they're basically walled off) except for the Grid Profile "1547:2015, No Export-WHB" of the system. I follow you regarding the frequency shift concept, the power curtailment, etc. - (I'm an Enphase certified installer). Trouble is that I want to charge the LLs from the micros, already have 10Ts in place and just wanted more run time without running 2 separate power systems.

 

[Gubman]

I may be misunderstanding your configuration - do you have gen port setup for AC coupling / microinverters, or are you treating the Enphase batteries as if they were a backup generator (no ac coupling)?

Yes setup for AC Coupling, treating the Enphase batts as a generator via AC coupling + power production happens here as well (via IQ8s). The Enphase system is more of a buffer at this point as I do not want to trash 40kWh of capacity.

 

[Gubman]

here's my attempt to do try another approach with a WX 6448 Pro https://diysolarforum.com/attachments/3master-wiring-schneider-off-grid-gif.123909/

 

[HighTechLab]

Treating them as a generator for AC coupling. Power production happens here as well. They're more of a buffer at this point as I do not want to trash 40kWh of capacity.

I think this is where I'm still unclear - if you are treating the Enphase as a generator, you aren't technically AC coupling with the 18kPV. The 18kPV appears as a load to the Enphase system. The Enphase system sets the frequency, the 18kPV would match it to charge the batteries, and the Enphase system would be responsible for frequency-shifting to regulate power on the microinverters. This is where I would not expect to see any power flowing from the 18kPV to the Enphase system - the 18kPV would be connected to the load side of the Enphase battery system rather than the grid side. This configuration would also keep the EG4-LL batteries full until power is lost due to the Enphase batteries turning off.

Otherwise, if you have the 18kPV configured for true AC coupling, the grid side of the Enphase system would be connected to the gen port - the 18kPV is what sets the frequency and when the EG4-LL batteries are full, the 18kPV would raise the frequency to slow down import from the Enphase batteries and microinverters. This configuration would not be able to prevent power from being drawn from the 18k if the Enphase battery system was programmed for "grid" charging.

So that we are on the same page now, which configuration truly represents your system? First paragraph above or second? Is the gen port connected to grid side or load side of the Enphase battery system?

 

[Gubman]

I think this is where I'm still unclear - if you are treating the Enphase as a generator, you aren't technically AC coupling with the 18kPV. The 18kPV appears as a load to the Enphase system. The Enphase system sets the frequency, the 18kPV would match it to charge the batteries, and the Enphase system would be responsible for frequency-shifting to regulate power on the microinverters. This is where I would not expect to see any power flowing from the 18kPV to the Enphase system - the 18kPV would be connected to the load side of the Enphase battery system rather than the grid side. This configuration would also keep the EG4-LL batteries full until power is lost due to the Enphase batteries turning off.

Yes the 18K becomes a load, just like any other load connected to the Enphase system. That's how it started (see 3Master GEN). I charged the 60kWh over several days this way (from 55% to 100%) - monkeying around with amperage, SOC settings on the 18K. So far, all was well. The intent was to set the Enphase system to "turn off" after say 40% of its depletion to hold a reserve.

 

[Gubman]

Otherwise, if you have the 18kPV configured for true AC coupling, the grid side of the Enphase system would be connected to the gen port - the 18kPV is what sets the frequency and when the EG4-LL batteries are full, the 18kPV would raise the frequency to slow down import from the Enphase batteries and microinverters. This configuration would not be able to prevent power from being drawn from the 18k if the Enphase battery system was programmed for "grid" charging.

I thought of this, but decided to possibly get there as a plan B, however the charging worked so well, I moved on attaching the LOAD port of the 18K to the house. That's where the back-feed surprise began (see 3Master with LOAD).

 

[Gubman]

this was the initial setup to charge from Enphase.. Performed as expected.

 

[Gubman]

This configuration experiences the GEN back-feed, from Enphase to 18K.

 

[HighTechLab]

I'm chewing on these diagrams, thinking about this a bit - didn't want you hanging in the meantime. I thought I saw the problem but realized an error I made reading the diagram.

 

[Quattrohead]

Bottom line is, the 18k should NEVER back feed into the gen port, that would make your generator dance and smoke.
Something is up with the gen port settings.
I can't really help anymore because I have not used the gen port yet.

 

[HighTechLab]

Does this backfeeding happen day and night or only during day, or only during night?

 

[HighTechLab]

Bottom line is, the 18k should NEVER back feed into the gen port, that would make your generator dance and smoke.
Something is up with the gen port settings.
I can't really help anymore because I have not used the gen port yet.

The thing is, a generator has nowhere for the power to go - the frequency would raise and that would trip things out. In this case however, there is an ac coupled ESS with more batteries that actually has a place for power to go and a control mechanism to pull power from ac coupled microinverters...that's what has caught my attention here.

 

[Gubman]

Does this backfeeding happen day and night or only during day, or only during night?

day & night, irrespective of any solar.

 

[Gubman]

The thing is, a generator has nowhere for the power to go - the frequency would raise and that would trip things out. In this case however, there is an ac coupled ESS with more batteries that actually has a place for power to go and a control mechanism to pull power from ac coupled microinverters...that's what has caught my attention here.

Initially since this worked, the 18K had a green generator icon, afterwards the icon went away in favor of the "HV power transmission pole". The EPS icon showed and power flow animation was going to that, no longer to the yellow house icon. That's the only clues I have so far. (I have disconnected the 18K LOAD at this time, house is back on Enphase LOAD until I get this worked out.)