[RE-wrenches] All-In-Ones / Sol-Ark fail

[Jason Szumlanski]

We have been talking a lot recently about all-in-ones. I just had a massive
fail during Hurricane Milton with a quad Sol-Ark 15K off-grid system that
deserves some discussion about whether AIO is a good idea if it can't build
in some resilience to errors. I'm not sure if the new Midnite unit is
better in this respect, but this is what happened to the Sol-Ark system...

Four inverters, each with 4 strings of PV paralleled to 2 MPPT per
inverter. One of the slave units developed some sort of PV DC fault during
the storm. This caused the slave inverter to shut down and throw an error,
which in turn caused a parallel fault across all four inverters. Power
output ceases at that point. Apparently the system keeps resetting because
I have a cell modem that uploads data to Sol-Ark, but that cell modem is
powered by the inverter outputs, so it must be getting power at least
intermittently. The rest of the loads are basically flatlined according to
the Sol-Ark data. It's mostly air conditioners, so they probably can't turn
on fast enough before the PV fault causes another shutdown.

So, in essence, one of 16 strings of PV develops a fault, and that causes
all four inverters to malfunction? What is the point of redundancy if a
fault of one results in a fault of all?! If there is a true PV input fault,
shouldn't that just shut down that MPPT, or perhaps all of the PV DC input
to that inverter? And why can't this inverter continue to invert power from
the batteries and charge from a generator when there is a DC input fault
that could be programmatically isolated and ignored?

This is a bad design in my opinion, and something I hadn't considered. If
the faulted inverter can't function with a DC input fault, it should just
take itself out of the game. (This is 120/240 split phase, BTW). Is this
how all AIO inverters work? One inverter fault on the DC side kills all
paralleled units' AC output? Not good.

This is a completely off-grid system on a remote island with no vehicle
access, so it's not exactly easy to do a "truck roll" on this one,
especially post-hurricane. To make matters worse, the generator was running
at the time of the fault, as it was being signaled to run because the
battery had reached the assigned charge voltage. The fault also killed the
2-wire start signal from the master, so the system also stopped passing
through generator power to the loads. The house is dark.


Jason Szumlanski
Florida Solar Design Group
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20241010/07122465/attachment.htm>