Applicability of feed-in limit in a mix SMA/Victron system

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Maciek Haranczyk asked Feb 24, '21

Applicability of feed-in limit in a mix SMA/Victron system

I would like to confirm with you that the recently added grid feed-in limit function would be applicable to my system. I cannot test it myself as I have not purchased all the hardware.

I have 3 grid-connected SMA inverters totaling 14kW while my house installation can handle 14.5kW max (63A/230V circuit breaker). I am looking to connect MultiplusII 5kW in grid-parallel configuration with additional PV panels connected via both DC-coupling and AC-coupling (Fronius) to mainly server the critical loads.

I understand that in order to export energy from Victron to the grid in a controlable way I will need to install Energy meters on both the main line and on SMA inverters for Victron to know the current grid load and PV/SMA production.

Now, I noticed that during off-summer months my SMA inverters rarely exceed 10-12kW production. I would like to know if I can use Victron and its grid feed-in limit to set the maximum feed-in of both Victron and SMA at exactly 14kW ? (i.e. top-off SMA production with Victron power, if I understand correctly Victron cannot regulate SMA in a grid-parallel setup, correct?).

In above is correct, question #2: In reality, how strict is the realization of feed-in limit ? Is it possible that the system will exceed the 14kW limit for a brief moment and trip the main circuit breaker (14.5kW) ?

Thanks.

ESS

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Answer 1 · 2021-02-27T22:01:09Z

jacola answered · Feb 27, 2021 at 10:01 PM

Hi maciek, dont expect wonders from a grid-parallel setup.

a) to control the production output of the SMAs, whatever interface will be used it won't function within few msecs. The SMAs can be controlled via Modbus/TCP, or via frequency shifting, but that only works if they are connected in island mode through the Multiplus - victron cannot change the grid frequency in grid-parallel mode ..

b) the question mainly will be how fast is your circuit breaker and how much tolerance will it give.

i have successfully managed to throw myself off the grid with a grid parallel system by just switching a high power load (water pump 7kw) on and off.
Energy meters like the Gavazzi ET340, but ANYTHING serial, outside of the multiplus, will probably take few tens to hundreds of msecs to be polled and read (modbus is 9600 baud ..). if you have, So your grid parallel ESS will overshoot significantly, and depending on your fusebreaker can be throwing you off quickly.
My advice (but i have to say i am not a victron expert, installer or the like) .. do NOT do grid parallel for that, you have a chance if you feed THROUGH the multiplus as it can react very quickly to load changes, but external meter .. slow boat (and with external control victron even limits the reaction of the multiplus to changes to 400W/second to my understanding for stability reasons).

So while my post doesnt exactly answer your question, you can probably get enough info to see that in grid parallel mode, fast control is impossible (in my view).

Johannes

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Answer 2 · 2021-02-28T10:51:04Z

Maciek Haranczyk answered · Feb 28, 2021 at 10:51 AM

Hi,

thank for feedback.

I see your point. I can just set up 'zero feed in' and forget about those few extra kWh...or buy a bigger battery :)

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