[RE-wrenches] Adding battery to grid tie

Sat Aug 9 16:40:02 PDT 2025

If you are using the inverter with nothing connected to the high-voltage DC
(PV) bus, AC Coupling is not recommended.

The MNP AIO can operate as a standard string inverter, with or without a
battery. Unlike most other AIOs, it can run with both a generator and
AC-coupled inputs at the same time (personally tested). However, the
AC-coupled input must be smaller (lower output) than the generator input;
otherwise, the generator may drop offline. This limitation is in place to
protect the generator’s control system.

A side note:

As with all inverters, firmware remains a major consideration. Fixes and
adjustments can sometimes introduce new issues. As inverter technology
advances—and with some states requiring utilities to control customer-owned
equipment—firmware complexity will likely continue to grow, creating
ongoing challenges for installers. We are all in for more challenges as we
move forward.

On Sat, Aug 9, 2025 at 5:27 PM Jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Thx William
>
> The instructions specifically say that AC coupling only is not
> recommended.
> To me I read that in terms of the inverter wanting DC solar as well
>
> Can you explain what’s going on.
> Which is the correct way to install it and why does it say not recommended
>
> Thx
> Jay
>
> On Aug 9, 2025, at 3:13 PM, William Bryce via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> 
> With the MNP AIO You can use an AC couple array at the same time as the
> Generator. But.... If the AC coupled input is larger than the
> Generator input, the Gen set relay will open to protect the Generator.
>
> 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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