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bipedalprimate avatar image
bipedalprimate asked

ESS Install - Use ET112 or CT?

Preliminary design of an ESS system is as follows:

1675299480082.png

Questions and assumptions:

  1. ESS documentation states that ESS system will not work with a Fronius Smart Meter, however, I suspect that only relates to when the Fronius inverter is located on AC Out and Cerbo is managing the Fronius inverter as a Micro Grid. Is that correct?

  2. Fronius inverter is not located on AC Out in this design because Multiplus II is not allowed to be Grid Interactive in Australia. Grid is quite stable so no pressing need for grid fail charging by PV.

  3. Fronius Smart Meter is used by Fronius inverter to limit export to 5kw. Location of Fronius Smart Meter with respect to ET112/CT in this design should allow that to continue when AC Loads & Battery Charging are less than 1kw. Is that correct?

  4. There are numerous threads on the ET112 vs CT on this forum and they suggest that:

    • CT provides a faster response by Multiplus II to changes in current flow compared to the ET112 although the Cerbo GX manual states the CT is the lowest cost but least accurate option. Is that correct and does that matter in this ESS design?

    • There is doubt about the ability to use a CT in a parallel configuration. Is that correct?

    • If a single CT in a parallel configuration is not workable, would 2 CT's each connected to the separate Multiplus II be allowed/work?

  5. In the Datasheet-Energy-Meters-Selection-Guide-EN-.pdf it states:
    "in an installation with a single-phase utility connection, that also has a PV Inverter that needs measuring with a energy meter, then you can use two pieces of ET112 or use the ET340."
    How would the 3 phase ET340 be wired and configured in the Cerbo GX?

  6. I suspect that the design as drawn above will not recognise the Fronius inverter on AC In (because no comms between it and Cerbo GX) and hence the suggestion to use 2 ET112's. Is that correct? If so, is there another way for the Fronius inverter to be recognised?


Needless to say, there are probably other factors not considered so if you have any input, please respond.

Multiplus-IIESSEnergy Meter
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datasheet-energy-meters-selection-guide-en.pdf (148.7 KiB)
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8 Answers
Rob Duthie avatar image
Rob Duthie answered ·

Hi

Only 1 CT ET112 per installation as the Cerbo takes control over the master and slave of a system.

As i have used 3x Multiplus2 in parallel with one CT ET112 to control a system

The ET112 is much more accurate than the internal CT and better control as it seeing all the load power than the internal one.

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bipedalprimate avatar image bipedalprimate commented ·

Thanks Rob.

I was contemplating using an external CT. Does your answer still apply?


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Rob Duthie avatar image
Rob Duthie answered ·

Yes it can, depends how far away the metering point is from the inverter. As i found the internal and the plug external CT a bit flaky in the readings. So have not used them since as always used the ET112 meter CT.

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bipedalprimate avatar image bipedalprimate commented ·

If I understand you correctly, you would suggest this:

1675313808303.png

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Rob Duthie avatar image
Rob Duthie answered ·

Hi

You don't need the VE meter ET112 on the Fronius output as it data is taken from the fronius smart meter directly and is used as required. As the Cerbo has WiFi and Fronius has WiFi they both talk together, and it just works well.

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cliff76 avatar image
cliff76 answered ·

@Rob Duthie , is the ET112 still required at the grid metering point? Or can both ET112's be done away with, since there is comms over the network between the Fronius and the Cerbo?

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Rob Duthie avatar image
Rob Duthie answered ·

Only 1x ET112 for the cerbo is required on the grid metering point.

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1234enough avatar image
1234enough answered ·

Had a et112, but changed it to a CT, as found the et112 was very laggy, CT responds faster but readings may not be as accurate

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cliff76 avatar image cliff76 commented ·
@1234enough Are your loads on the outputs of the MP? or are they on the Input side ( parallel to the MP )? Did you remove the ET112 completely?
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1234enough avatar image
1234enough answered ·

Most loads on AC in side, with dump loads on AC2 out.

ET112 removed completely, after I trialled CT clamp, which I found to be much faster reacting to load variations.

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cliff76 avatar image cliff76 commented ·
@1234enough Would you mine sharing a diagram of your set up? I'm also trying to set up my system with just the CT clamp, but i can not get it to work. Whenever the Fronius starts to produce power over and above the load draw, then the MP will disconnect from the grid.

I dont have any of my loads on the AC output like you. All loads are on the AC input, with my CT clamp on the incoming grid tail.

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1234enough avatar image
1234enough answered ·

Diagram not required, MP2 AC in connected to house DB in the same way as any of the other circuits in the DB, CT clamp on incoming + tail between supplier electric meter & DB plugged into MP2 "K" external current sensor 3.5mm jack socket.

ESS assistant.loaded and running.

Dump loads connected onto AC2 , switches on with relay assistant.

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