Hi all,
I’m writing this in the hope that it’ll help others to figure out why their own Fronius AC PV arrays mysteriously fail to ‘throttle’ properly since mid October!
Background
Here in Australia I’ve been working for a few years now on an energy management system (energyautopilot.com) and as part of that, I’ve been (of course) using my own home Victron Energy system as a test site 
(Yes, I’m fully aware of DESS but what we are developing is multi-vendor, multi-retailer, it overlaps with what DESS does but it does more than that)
My house is a conventional (but large) system : Three phase grid connection , 3 x Multiplus 15k units into 60kWh of Pylontech batteries and around 15kWp of solar panel strings in to three Fronius AC PV inverters.
The Victron system controls the Fronius units in the usual way, via MODBUS, for monitoring and throttling of power output levels.
I need to be able to have the Victron system properly implement grid feed in control (e.g. to set the system to be ‘zero export’ at various times) and at other times I want to turn the solar entirely off - all of which works just fine via mqtt control operations I’m using to talk to the GX.
The problem
Around October 19, all the solar control from the GX just stopped working. And stopped working in a strange way… the Victron sends the control commands, the Fronius inverters show up on the GX as being ‘throttled’ (as expected) but the throttling just silently fails to happen! Instead, the PV is running at full power all the time.
No error messages, no apparent faults, but - also - no control! I have been scratching my head about this ever since - for weeks, I could just not fathom what’s gone wrong. At last, though, I found it.
The solution
It turns out that I have got automatic updates enabled on my Fronius system, and in mid October, a Fronius update turned on a flag that I don’t think previously existed on my system (see screen shot below). This is in the “DNO” editing page…
This control setting is not one I was previous aware of. I think (but I’m not sure) that the setting might not have previously existed in the web user interface at all.
In any case, it is there now, and the checkbox was on. As per the documentation in the image above, having this on actually results in total loss of direct MODBUS based control over the inverter power output. And that loss of control is silent (and deadly ).
I turned this checkbox off and - bingo - regained control over my Fronius PV output levels from the Victron GX once more.
So I’m writing this all down in the hope that it helps other people who might be wondering why their solar throttling has silently broken in Australia since mid October.
A few consequences to mention:
- I have turned off automatic Fronius software updates!
- I would suggest to Victron Energy that it would be worth enhancing Venus so that it not only enables throttling but so that it checks to see if it actually works, and so that Venus raises some sort of alert if there is a sustained period in which throttling is enabled but the actually measured output is far in excess of the amount specified in the throttling control loop.
Best wishes,
Simon Hackett