[RE-wrenches] Adding battery to grid tie

drake.chamberlin at redwoodalliance.org drake.chamberlin at redwoodalliance.org
Mon Aug 11 06:35:41 PDT 2025



I use the Sunny Island designation of "Protected Loads."

---

On 2025-08-09 13:54, jay via RE-wrenches wrote:

> Yeah I've given up trying to correct people on that one.
> 
> On Aug 9, 2025, at 11:26 AM, Foxfire Energy via RE-wrenches 
> <re-wrenches at lists.re-wrenches.org> wrote:
> 
> 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
> 
> -------------------------
> 
> 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 [1]
> 
> On Sat, Aug 9, 2025 at 9:50 AM david quattro via RE-wrenches 
> <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> 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> 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> 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 [1]
> 
> On Sat, Aug 9, 2025 at 8:26 AM Jay via RE-wrenches 
> <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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