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

[Chris Sparadeo]

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> 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
>
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