[RE-wrenches] off-grid AC coupling feasibility

[Kirk Herander]

Jerry-
The pole mount does not exist for a few more weeks, so I have time to think
about DC or AC coupling for it only. To clarify, the old roof 1.8 kw array
is functional and has been charging the new blue ions through an old
Outback pre-hub 60A controller(replacing it soon with a new FM60). So I do
have existing dc-coupling already to get around dark start issues for the
most part.

Right now I'm starting to lean towards 100% DC coupling, hooking the new
pole-mount array to an OB FM100 300vdc max 100A charge controller *IF* I
can find one in time. At least then I can see everything on one dashboard
(OpticsRE). Both Mate3s and hub 10.3 are already installed.

One of the other things influencing my decision is the request from my
customer to have it "grid-ready", which to them means the house is easier
to sell when the time comes, if the buyer wants to bring in the grid power.
I won't go into it, but it is a simpler solution (in terms of local
hardware requirements) to AC-couple the new array with these utility rules
in mind.

So there is no fits-all solution to AC vs. DC coupling, as someone said.

On Sat, Jul 30, 2022 at 3:58 PM Jerry Shafer via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Its not clear to me if you will actually have a DC side coupled connection
> in talking about the pole mount. If so then it does work but if not then
> no, the big question is how would you restart the inverter to restart the
> SE to start the charging process on the AC side, answer, you can't in most
> cases. Example, SMA SI coupled with SMA 4K's, you have a dead battery, you
> need to bring up the VDC to wake up the inverter to wake up and count down
> the 4K's the trick here is to alter programming to instant start the 4K
> upon getting VAC and hertz instead of the 300 sec count down. Something
> else,  LFP does not relax and get any parasitic voltage back to even start
> the SI so changing the timers may still not work. Best bet is to have at
> least some DC side PV to charge a dead battery without the inverters at
> all. I did ac coupling with Trace and SMA 20 plus years ago and SMA said
> then it was not possible. How the world has changed. fun times!
>
> On Sat, Jul 30, 2022, 9:31 AM Kirk Herander via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> All,
>> Anyone out there successfully AC-coupled inverters in an off-grid system?
>> Advantages vs. pitfalls?
>>
>> In my case I'm thinking of its practicality with a Solaredge inverter
>> AC-coupled to an OB Radian inverter. OB firmware makes this pretty easy
>> now. So effectively the Radian is always operating in a grid-backup mode.
>>
>> I already upgraded the system to the Radian, and soon to add 5kw of
>> pole-mounted PV(currently only 1.8kw of 22-year old PV on the roof). This
>> system also just got 16kwh of Blue Ion LFP batteries.
>>
>> This is a last-minute thought I have instead of investing in additional
>> DC charge controllers for the new array.
>> Cost-wise there's not much of a difference between several high-quality
>> charge controllers and a smaller SE inverter w/optimisers. Thanks.
>>
>> --
>>
>> *Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*
>>
>> *Owner|Principal, VT Solar, LLC*
>>
>> *Celebrating our 31st Anniversary 1991-2022!!*
>>
>> *www.vermont.solar*
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>>
>> dba Vermont Solar Engineering
>>
>> 802.863.1202
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-- 

*Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*

*Owner|Principal, VT Solar, LLC*

*Celebrating our 31st Anniversary 1991-2022!!*

*www.vermont.solar*
<https://nam02.safelinks.protection.outlook.com/?url=www.vermontsolarnow.com&data=02%7C01%7C%7C9f0330d75a244870112408d685311841%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636842843233477645&sdata=0NjyuKeQbEK6245SNnk8X4XnP9Q%2B%2BqtvcALkdDghvk4%3D&reserved=0>

dba Vermont Solar Engineering

802.863.1202
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