[RE-wrenches] Dual Sol-Ark - not paralleled - backing up separate 200-amp panels, with one AC-coupled input:

Fri Oct 24 10:44:28 PDT 2025

Your answer is appreciated and acknowledged.

When I posted this, I 99.999% expected the answer would be: "Ummmm, of course you can't do this (dummy)" and the  real value has been reading some options from you all.

Think I'll be combining the two panels via 400-amp disconnect for a single service entrance, paralleling the two Sol-Arks/Homegrid batteries, and adding a grid-tied PV inverter at the array and use the inground conductors to AC-couple to the paralleled Sol-Arks.

Howard "Scot" Arey
Owner, Solar CenTex
254-300-1228

________________________________
From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf of Poole, Jharen via RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Friday, October 24, 2025 9:09 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Poole, Jharen <Jharen.Poole at sol-ark.com>
Subject: Re: [RE-wrenches] Dual Sol-Ark - not paralleled - backing up separate 200-amp panels, with one AC-coupled input:

Having the inverters operate unparalleled with a single AC coupled input is not a recommended configuration for an installation that I would give. In this setup, the inverters can conflict with each other, leading to unstable or abnormal behavior in the system operation and the data being reported.

While I haven’t personally encountered this exact configuration in the field, similar cases have shown that, at best, it results in no operation for the AC coupled source, erratic inverter performance (Inverters constantly fighting for the power, resulting in unstable amperage draw or issues with syncing), and in more severe cases the inverters fail to operate with each other resulting in potential equipment damage.

To address your question about the frequency shifting, if the inverters were to reach this stage without tripping a fault, there would likely be a heightened risk of phase and frequency instability. Ideally, the AC-coupled source would shut down, but the Sol-Ark inverters could potentially enter a loop where significant damage may occur.

Best Regards,

Jharen Poole
Applications Engineer II
972-575-8875
[cid:0c4ed8fc-b5ea-4f39-883c-c4dc4d6d3821]
________________________________
From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf of Howard Scot Arey via RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Wednesday, October 22, 2025 2:47 PM
To: Chris Sparadeo <sparadeo.chris at gmail.com>; RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Howard Scot Arey <scot.arey at solarcentex.com>
Subject: Re: [RE-wrenches] Dual Sol-Ark - not paralleled - backing up separate 200-amp panels, with one AC-coupled input:

Caution: This email is from an external source.

Thanks for everyone's feedback and can't say any is unexpected. Combining the loads and paralleling the SolArks might be best but would allow me to share the ac-coupled GTI input to both via a de-agg panel.

Howard "Scot" Arey
Owner, Solar CenTex

NABCEP PV Installation Professional
TECL 29755
254-300-1228

________________________________
From: Chris Sparadeo <sparadeo.chris at gmail.com>
Sent: Wednesday, October 22, 2025 1:50:44 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: scot.arey at solarcentex.com <scot.arey at solarcentex.com>
Subject: Re: [RE-wrenches] Dual Sol-Ark - not paralleled - backing up separate 200-amp panels, with one AC-coupled input:

Hi Scott,

About a year ago I backed up two separate 200A panels on a 320A service with two separate Sol-Ark 15K units and two separate battery banks. Although the separate systems functioned just fine, I was getting really crazy power flow data in the app. Sol-Ark tech support suggested that I combine the two systems (combine the battery bank and AC input/output). Apparently, upstream PV production can adversely affect the downstream system’s monitoring. Luckily, the electrical layout of the existing infrastructure allowed for me to combine the two systems fairly easily. After I combined everything, the monitoring issues cleared up. The PV in this case was DC connected and evenly split between the two inverters. But I could definitely see an AC connected PV system causing headaches with the other system when it goes to frequency shift it’s connected PV production.

The other thing to keep in mind with separate systems is that if a generator is connected, controlling it from both inverters is clunky and using only one system to control the generator leaves the possibility that the other might turn off from low SOC before the generator turns on. But it sounds like you are talking about a grid tied system with AC PV input, so I’m thinking a generator probably isn’t at play.

I’d be curious to hear what Sol-Ark tech support has to say about your configuration and if they would also suggest combining them.

Best,

Chris

On Wed, Oct 22, 2025 at 1:52 PM scot.arey--- via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
Background: New customer wants both 200-amp panels backed up and neither can be "slimmed down" to allow just one backup panel so looking at dual, but not paralleled, SA15 (or 18).

The design / cost-reduction opportunity: There is one 100-amp set of inground conductors already going out to where ground mount would be. My immediate thought is to use this wire already in ground to transport output of solar ground mount. I'd put a large grid-tied inverter at the ground mount and "de-aggregate" the AC via a load center by the Sol-Arks, and AC couple half to each Sol-Ark. No trenching...both Sol-Arks have AC-coupled input

The question I need help/ideas on: What happens to frequency shift if just one Sol-Ark /battery combo is near-full SoC during backup ops and shifts to 62hz to shutdown the AC-coupled GTI. Seems it would shift the ac-couple POI to 62hz but the other inverter would still be at 60hz still and this conflict might not "mix well" getting back to the grid-tied inverter at the ground mount.

I may well come back to the option of new trenching and pulling separate DC conductors to each Sol-Ark and get the simplest, least complex design but I'm exploring all design options to use existing wire and not have to trench.

Best analogy I can come up with, is that like an Outback system having "float charging coordination," I could have "freq shift coordination" between the Sol-Arks and of course that is not a feature in non-paralleled inverters.

I suppose combining the separate 200-amp services and then paralleling the Sol-Ark inverters to this might be the necessary actions if I want to avoid trenching and still back up all.

Howard "Scot" Arey
Owner, Solar CenTex

NABCEP PV Installation Professional
TECL 29755
254-300-1228
[cid:ii_19a0d34c7974bb066c91]

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