[RE-wrenches] Adding battery to grid tie
Christopher Warfel
cwarfel at entech-engineering.com
Mon Aug 11 15:47:23 PDT 2025
That part about utilities controlling the systems caught my eye. Most
Utility Commissions are in the pocket of the utilities in my opinion. In
Rhode Island, it is almost impossible to get intervenor status. Then
you are relegated to Public Comment. The "Consumer Advocate" has never
in my memory in30 years advocated on the side of the "consumer".
I will tell you that in this State, the utilities think they own your
investment, and Block Island Power Company's Jeff Wright President (from
Velco}, and the Chair of the Board MacMullan presented extremely poor
analysis to change the customer generation policies. The PUC yawned and
gave it a pass. They didn't even investigate the analysis. The utility
based it all upon ONE customer, while I presented a amalgamation of 15.
Not even discussed.
So, if you have such a similar Commission, you need to make sure you do
as much public outreach to more the chains. We are so small, it is just
about impossible. Chris Warfel
On 8/9/2025 7:40 PM, William Bryce via RE-wrenches wrote:
>
> 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 <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> 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
>>>>> <http://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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--
Christopher Warfel, PE
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
(401) 447-5773
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