Zero Feed-In ESS - Weird (or normal) behaviour

DIY
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Hi,

I am seeing some weird (or not what i expected) behaviour from ESS/Zero Feed-In which I just want some clarity on. I will try and explain as best i can.

General Setup:
2x MP2, 2x 15Kwh battery (jkbms in parallel bms.can), cerbogx etc etc. 2x Gen24 AC-In side, 2x MPPT DC side. ESS configured to power all system loads etc. Grid set-point is 20w normally. ESS configured without battery life. Victron smart-meter installed.

Issue:
I am pulling FIT price from local suppliers API. When FIT goes negative, i am writing modbus register via NodeRed to limit ESS grid feed-in limit configuration to 0w. If FIT is positive, we set feed-in at 10kw etc. Both feed-in AC and DC switches are turned on. Generally it works well if FIT price goes negative post battery being fully charged… However…

If the battery is charging and there isnt yet full PV power to reach the CCL as received from the BMS, and if the feed-in limit is triggered, the fronius PV will throttle back to ensure there is no excess to the grid. The battery will keep charging but wont ‘request’ any more current even though there is move PV available as the sun rises etc. As an example, prior to FIT going negative, it was charging at 60amps but never goes any higher while the feed-in limit is active.

Its like the battery isnt able to demand more load/charge and is somehow also throttled also…

Also, if the feed-in limit is active and there is a new AC load demand on the AC-IN side, the multi will drain the battery before it ramps up the PV from the Fronius (AC-In Side). Is this normal?

If we turn the feed-in limit off, then the PV/MPPT ramps up suppling the loads and increasing the charged current to the battery.

My expected behaviour
What I expected was that if feed-in limit is active, that any new AC load on either the AC-In or Out side will trigger the PV/MPPT to throttle up to supply the loads. Also, if the SoC is < 100% and the battery is expecting a charge, that it will draw as many amps as it can from the PV before throttling it back. ie, throttling should be the last priority over any other load or charge demands from the ESS.

Is this expected or could this be a configuration type issue (or lack of understanding).

Thanks in advance for any guidance here.

Cheers,
Evan

2

Ok, so this was a ‘user error’ and my lack of understanding of how ESS feed-in works.

My original understanding was that if the FIT price was negative, that we enable AC/DC feed-in excess and configure a feed-in limit of 0, that ESS will adjust the PV output to match the loads whilst curtailing any excess PV feed-in. This is not the 100% the case. It will behave as my issue first described.

The solution was to disable AC/DC PV excess feed-in when the FIT was negative. This allows the PV to use as much power as the loads demands including any charging. Anything in excess of this is curtailed on the basis of the AC/DC switches being disabled. This is the behaviour I was looking for.

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Interesting, I would also expect that - in a limit situation - available PV is used to supply loads and production of pv inverters is increased as loads increase.

Second time i’m reading about this issue.

Would be interesting to know, how it behaves with a Feed-in limit different from 0, say 500W.

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I can certainly give it a try and update the thread

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