[RE-wrenches] Adding battery to grid tie

Sat Aug 9 13:02:14 PDT 2025

I don't think any AIO manufacturer recommends AC Coupled only. Tesla,
oddly, specifically markets adding Powerwall 3 to existing solar. Franklin
fully embraces AC Coupling for obvious reasons.

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

On Sat, Aug 9, 2025 at 3:12 PM Jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Thx I looked it up.
> But according to midnite they don’t recommend a only ac coupled system.
>
> Jay
>
> On Aug 9, 2025, at 12:53 PM, Dave Tedeyan via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> 
> The Midnite Power AIO has inputs for grid, generator, AC coupling and
> another smart load. I have not used both generator and AC coupling to see
> how it acts if both are active at the same time, but at least the inputs
> are there for them both.
>
> On Sat, Aug 9, 2025, 2:33 PM Jerry Shafer via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> Jason, Wrenches,
>> Consensus well that may not be the correct word to use, personally l have
>> used Solark for retrofitting systems that already have GT type inverters,
>> if you go with AC Coupling then the gen set connection is a little more
>> complicated but very doable.
>> Funtimes
>>
>> On Sat, Aug 9, 2025, 11:26 AM Jason Szumlanski via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>>> I go with "Backup Loads" on my drawings.
>>>
>>> Tesla will not charge from a generator. But you can obviously have a
>>> generator power the loads via a transfer switch if the battery is
>>> completely depleted. It's not the best solution, for sure.
>>>
>>>
>>> Jason Szumlanski
>>> Principal Solar Designer | Florida Solar Design Group
>>> NABCEP Certified Solar Professional (PVIP)
>>> Florida State Certified Solar Contractor CVC56956
>>> Florida Certified Electrical Contractor EC13013208
>>>
>>>
>>> On Sat, Aug 9, 2025 at 1:57 PM jay via RE-wrenches <
>>> re-wrenches at lists.re-wrenches.org> 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
>>>>
>>>>
>>>> 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
>>>>
>>>>
>>>> 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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