[RE-wrenches] off-grid AC coupling feasibility

[Jerry Shafer]

An all DC side charging is preferred and will have the simplest charging
system. Flex net DC shunts, easy to monitor.  Last l heard FM 100 were
pushed out till late in the year
Fun times

On Sat, Jul 30, 2022, 1:37 PM Kirk Herander via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> 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*
>>> <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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>
> --
>
> *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
> _______________________________________________
> List sponsored by Redwood Alliance
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