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Jim Ryan avatar image
Jim Ryan asked

Zero Export For DC Coupled System with Cerbo GX

I am designing a grid-connected, self-consumption, DC-coupled system with the following components:
- Cerbo GX
- two Quattro inverters
- SmartSolar MPPT Can charge controllers
- Miasole CIGS thin-film ‘Flex modules’
- LFP batteries with BMS and closed-loop communications

But NO FRONIUS INVERTER or other AC-coupled inverter....simple DC-coupled with Victron components.
My question is, can the system as described above be configured to provide Zero Export to the grid, ie after loads are satisfied and batteries are fully charged? Can the Cerbo GX and ESS provide reliable zero export?

After reading and re-reading the ESS Design and Installation Manual it’s very clear how an AC-coupled system can work to provide zero export.....but it is much less clear about a DC coupled system. It suggests it can provide zero export, even without the addition of a separate AC grid meter, but it does not say that explicitly. I need to know if the Cerbo GX can handle this, ie provide zero export or grid feed-in, as I really don’t want to have to buy and integrate a separate third-party zero export device.
Thank you Community...
Jim

cerbo gx
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1 Answer
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Jim Ryan,

Yes, this works as expected.

There is a menu on the GX device called ESS, and there you can enable or disable grid feed-in for AC and DC solar independently.

In this screenshot the DC-coupled PV feed in excess is enabled, but you would want to disable it;

cleanshot-2023-03-06-at-150424.jpg


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Jim Ryan avatar image Jim Ryan commented ·
Thank you Guy....I enjoy your videos...nice to see your prompt response.

FYI, the grid feed-in is split-phase, 225 amps, so I will need a separate grid meter (EMS24) with CT's to provide meter data to the Cerbo GX, especially as my two Quattros do not receive all AC input from the grid.
I think I understand how to do this now....although I must say, the ESS Design and Installation Manual seems very 'slanted' toward AC-coupled info while the DC-coupled part is confusing. In my opinion anyway, after reading and re-reading half a dozen times.
Thank you again.....
Jim

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rickc avatar image rickc Jim Ryan commented ·
For split phase 225A, the only energy meter I considered is the Carlo Gavazzi EM530, directly supported by the Cerbo gx. This is because the EM540 has internal passthrough, and cannot do that many amps. Same with the new Victron energy meter. I did have to find my own 5A CTs to go with it, and set the CT ratio to 40 which is good to 200A.


Note that when heavy loads switch off, there is still some pushback onto the grid.

It cannot respond fast enough to prevent that.

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clay123 avatar image clay123 commented ·

Hi @Guy Stewart (Victron Community Manager) ,


I have a similar situation with my dc coupled system - the system consists of:

- 2 x smart solar RS450/200

- 6 x Multiplus ii 48/5000 (2 per phase)

- CCGX

- BYD batteries


System is connected to the grid for battery charging but I do not want to export any power into the grid. If I disable the DC-coupled PV feed-in excess would it solve this ? Or will there be a bit of export still ?

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ clay123 commented ·

Hi @Clay123

There isn't any grid export by default, you need to manually enable it.


If you do enable the ESS mode - then it's possible there is some back feeding, even when grid export is disabled.

This can occur when the battery is full, and there is a large load being provided by a large solar array. If the load suddenly turns off, some of the surplus power from the PV array may cause a moment of back feed to the grid. Note - the MPPT RS are VERY fast to respond to this, so while technically still possible, it's unlikely.

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clay123 avatar image clay123 Guy Stewart (Victron Community Manager) ♦♦ commented ·
Thanks for your response @Guy Stewart (Victron Community Manager) .

In addition - is it possible to not enable ESS mode ?

I am looking to have a self-consumption system, where PV is prioritized and grid will only be for charging the batteries & supplying load when there is insufficient PV or battery charge (back-up).

I do not want any grid feed-in/export. I have installed a grid protection relay on the grid-side for isolation of the system if there were to be a grid-outage. But this does not control the export of excess PV generated. As you mentioned, there isn't any grid export by default - are there certain parameters that shouldn't be enable for it to operate in this manner ?


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pdsmith2147 avatar image pdsmith2147 Guy Stewart (Victron Community Manager) ♦♦ commented ·

We are also experiencing issues with quite a bit of export with MPPTs set to zero feed in. In a week we've export 2 days worth of energy. We've tried raising the grid set point but doesn't seem to have much impact.

Any help appreciated.



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