ESS with "inverse power assist"?

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petajoule asked Sep 23, '20

ESS with "inverse power assist"?

Is it possible to have an ESS configuration, where grid is used as "power assist" if inverter loads go over a certain threshold?

Client wants a 3p Multiplus-II system, and 5kVA per phase is ok 99% of the time, there is a 3x16A grid line serving only as fallback. No feed-in and usually also no draw from grid (in said 99% of the cases).

As the client is reluctant to go for a 8kVA or 10kVA 3p Quattro configuration (mainly because the higher self-consumption of the devices), the question is if the grid could be used as "power assist" in those 1% peak cases.

I was thinking of an assistant activating the transfer switch if load went over xx%. Possible?

ESS powerassist

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Answer 1 · 2020-09-23T09:04:12Z

ejrossouw answered · Sep 23, 2020 at 09:04 AM

@PetaJoule I cannot personally comment on 3-phase specifics, although don't see why it won't work in the same way. My 1-phase ESS is connected in parallel (only via the ACIN) and works in this way. No feed-in etc. At 10:00am you can see the inverter capacity was exceeded and the power requirements were simply complimented with power from the grid. The other grid consumption is scheduled charging off-peak.

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petajoule commented · Sep 23, 2020 at 12:48 PM

Not sure if the graph shows what you are saying it shows. Care to post the advanced view of AC-In and AC-Out (and the Inverter specs) for the time Sep, 22nd 9-11 a.m. ?

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Answer 2 · 2020-09-23T13:52:15Z

ejrossouw answered · Sep 23, 2020 at 01:52 PM

@PetaJoule As I said, it is ONLY connected on AC1IN. I am confident to say it does not matter whether loads are connected to ACOUT1 or ACOUT2, but stand to be corrected.

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petajoule commented · Sep 23, 2020 at 02:11 PM

You write your 1p-system is connected in parallel - so you have 2 Multi 3kVA or which ones? You do see a short overload before the transfer switch gets activated?

Unfortunately, the Victron docs do not shed much light on this matter also:

Notes with regards to the Input current-limit and PowerAssist:

Input current-limiter setting - The configured limit is used as the threshold for AC current at the AC-in of the Multi/Quattro. Further notice that:

Loads in parallel with the Multi/Quattro are not taken into account: therefore, install all loads on the AC-out of the Multi or Quattro in systems that require AC Input Current limiter functionality. For example - systems with a small AC load connected.

The current limiter will be used for both directions of the current.

The PowerAssist setting in VEConfigure3 will be disabled and ignored when ESS is installed.

The Dynamic current limiter in VEConfigure3 will be disabled and ignored when ESS is installed.

Probably using ESS in the first place isn't the best idea to start with for the planned system, as it is an "intentional islanding" scenario.

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ejrossouw petajoule commented · Sep 23, 2020 at 05:21 PM

My single inverter is connected in parallel to the household loads. There is never an overload on the inverter as it simply delivers to it's max and then add the grid as necessary. I only use current limit to prevent my Multiplus II 5kVA from overloading the 16A circuit until an upgrade to 20A is complete ;)

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