[RE-wrenches] off-grid AC coupling feasibility

Jerry Shafer jerrysgarage01 at gmail.com
Sat Jul 30 12:58:02 PDT 2022

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!!*
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