[RE-wrenches] Adding battery to grid tie

Sat Aug 9 10:26:11 PDT 2025

Umm, just an FYI, I actually got dinged for labeling the AC output panel from a battery backup inverter as "Critical Loads".. Critical loads (Critical Branch circuits) are defined in article 100 of the NEC as circuits associated with Patient Care.. AC loads from battery backup inverters are more appropriately defined as "Dedicated Loads"..
Maybe someone could correct me here, but I'm under the impression most garden-variety inverters are not rated for Critical Load applications.
db
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From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf of William Miller via RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Saturday, August 9, 2025 1:03 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: William Miller <william at millersolar.com>
Subject: Re: [RE-wrenches] Adding battery to grid tie

Correct me if I'm wrong:  I believe AIOs can accept AC coupled power through the load ‘output’ port. That leaves the Grid and Gen inputs free for their roles as labelled.

The AC coupled inverters connect via a breaker in the critical loads panel.

William Miller
Miller Solar.com
805-438-5600
www.millersolar.com<http://www.millersolar.com>

On Sat, Aug 9, 2025 at 9:50 AM david quattro via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
True.  if you want to do grid, gen, and AC Couple then you need a transfer switch or contactor.
       Likewise I haven’t touched a Powerwall, nor an Enphase battery.

On Sat, Aug 9, 2025 at 9:36 AM jay via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
One big issue with the AIO’s is that you can’t do grid, generator and ac coupling to the best of my understanding

I do like the idea of just removing the old GT inverter and stuffing that into the AIO, elegant

yes its my understanding that Tesla won’t accept generator.  While many are pissed off at eg4, I won’t touch tesla.

and FYI you can buy the same inverter at Fortress.

thanks everyone.

jay

On Aug 9, 2025, at 10:28 AM, Tyrone Houck via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:

Midnite AIO and Sol-Ark both work great for AC coupling in my experience. If anyone is new to "All In One" inverters I recommend having tech support walk you through commissioning, check firmware, etc. the first time.

On Sat, Aug 9, 2025, 8:47 AM William Miller via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
Two options:

1. AC couple existing inverter to a battery capable inverter.

2. Replace existing inverter.

I favor option 2.

Option 1 is only preferred if gaining access to the existing inverter for replacement is difficult. An example would be a micro-inverter system.

New AIO inverters allow true high voltage PV input so the existing stringing will probably not need to be modified.

I’m new to this so type of upgrade so I welcome any corrections to these opinions.  I did replace a Sunny Boy in my shop with a Soul Ark and it’s working great!

William Miller
Miller Solar.com
805-438-5600
www.millersolar.com<http://www.millersolar.com/>

On Sat, Aug 9, 2025 at 8:26 AM Jay via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
Is there a consensus as to what equipment to use for adding battery backup to normal GT inverter?

I’ve had a few people ask and I actually haven’t done it.

Thx
Jay

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