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Limitation to AC coupling with EG4 18K, help required...

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Vince Mex

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Nov 8, 2019
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Hi

I am in talk with EG4 to finc a way to AC couple my current 9.75 kwh array with Fronius Primo 11.4 with new 18 kwh array and the EG4 18K inverter.

Seems easy, plug the existant 9.75 kwh of the fronius on the Generator Input of the EG4 18K and voila (need to set the fronius into micro grid mode to be able to receive frequency shift from the 18K as well but that is a detail) BUT it finally CAN NOT WORK AS EASY AS IT SEEMS.....

EG4 just told me (and thanks for them for being honest) that in that case the system can not use the 200 amp pass through when ac coupled and then you are always limited to....12 kwh output of the 18K....and that you can not export to the grid as well because "The 18K has a 2 poles internal relay that switches back and forth btw GRID IN, GEN IN and LOAD OUT. It is able to utilize 2 of these simultaneously : GRID/GEN (well you can only charge up batteries then, not your load...), GRID/LOAD (ok but then the 9.75 kwh array power....is lost) or GEN/LOAD (Nice you enjoy the power of the grid tie system, the new system.....but are limited to 12 kwh of total output....)

So yes AC coupling looks nice with 18K......until you never exceed 12 kwh of loads...if you exceed that you are DONE.

Does any expert (that i am not....) has an idea of how to manage to enjoy the power of the 2 arrays powering up the loads first, charging then the battery pack and then export to the grid. I was thinking to put a second 18k but then the cost is exploding....

I can renounce to export to the grid because with near 28 kwh of array and 60 kwh of battery i could be good anyway and in this case 3 EG4 inverters 6000 XP....that would set the bar up to 18 kwh of output.....but how to join this system with my 9.75 kwh grid tie array in order to use the power from the grid tie system first....then the power of the new 18 kwh array and then charge the battery pack....and in case of grid down how to avoid that the grid tie inverter restart seeing the power from the 3 pcs of 6000 xp....

I am lost....

Thanks
Vince
 
If you were to use an inverter that AC couples to the Load Output of the inverter (not the Gen input) via a breaker in the same main or subpanel. Then it should be possible to consume 100% of both AC coupled power as well as the full output of the inverter, either AC pass-thru or battery power.
 
BentleyJ said:
If you were to use an inverter that AC couples to the Load Output of the inverter (not the Gen input) via a breaker in the same main or subpanel. Then it should be possible to consume 100% of both AC coupled power as well as the full output of the inverter, either AC pass-thru or battery power.
Click to expand...
Agreed, this is the standard way to do it, before Sol Arc put the AC coupling function on the AC2 input.
 
Just set up the EG4 18K as an off-grid system but with grid assist and let your present system feed the grid and make you money, it can still feed the EG4 with your own power if it ever needs help. Easy peasy.
 
Maybe @millsan1 can chime in on this. I think he is set up like you want to be, with no problems. He’s 24kw total/ Growatt ac coupled to 18Kpv.
 
Are you wiring the 18 in as whole house backup or just back feeding?

If just back feeding, then yeah, this makes sense.

If whole house, then it does not.
 
@Vince Mex

The inverter can accept PV solar inputs to both MPPT channels and AC coupled solar input at the same
time. The AC coupled solar input can be up to 90A of AC power or 21.6kW of solar. The MPPT channels
can handle up to 18kW of solar, with 12kW available for back feeding the utility grid. Therefore, up to
33.6kW of AC power could be sent back to the grid. For this amount of back feed, users will need either
a feeder tap or supply side tap as the point of utility interconnection. (See Diagrams 4.3 and 4.4 for more
information) The existing solar system is connected to the inverter's GEN terminal. For AC Coupling
wiring configuration, see Diagram 4.9.


I don't really see the problem here. It will pass all the fronius output to the grid after loads are satisfied and battery is charged.

It will only pass 12kw to the grid from the internal mppts but with 18kw connected or a 1.5 ratio, you are not losing that much production. Maybe 10kwh a day in the cooler months? If you don't want to lose anything at all, move one string from the mppt to a second grid tie inverter.
 
Last edited:
It is a whole house system. And the problem is that EG4 told me that the grid pass through is NOT working when the 18K is AC coupled with the generator port. Its internal relays has only 2 poles so it is GRID/GEN, GEN/LOAD or GRID/LOAD so you can not pull in extra power from the grid if your solar array is not enough because there is only these 3 modes....it seems to be either pulling all from the solar or all from the grid but not mixing bother in case the 18 k is AC coupled with the GEN Input. By the way is there any other solution to AC couple the 18K ?

I see only the Victron Quattro able to do so....but it is much more expensive, needs 2 units to get AC240V and also need add some solar charge controller for....18 kwh of panel so basically it doubles the cost or more...

I am ok to loose the possibility to inject to the grid and built the 18 kwh array system with the 18k inverter apart from the 9.75 kwh grid tie system.....BUT i do not know how to make them work in the same house without troubles.....

Sorry for my basic questions, i am no expert
 
1201 said:
@Vince Mex

The inverter can accept PV solar inputs to both MPPT channels and AC coupled solar input at the same
time. The AC coupled solar input can be up to 90A of AC power or 21.6kW of solar. The MPPT channels
can handle up to 18kW of solar, with 12kW available for back feeding the utility grid. Therefore, up to
33.6kW of AC power could be sent back to the grid. For this amount of back feed, users will need either
a feeder tap or supply side tap as the point of utility interconnection. (See Diagrams 4.3 and 4.4 for more
information) The existing solar system is connected to the inverter's GEN terminal. For AC Coupling
wiring configuration, see Diagram 4.9.


I don't really see the problem here. It will pass all the fronius output to the grid after loads are satisfied and battery is charged.

It will only pass 12kw to the grid from the internal mppts but with 18kw connected or a 1.5 ratio, you are not losing that much production. Maybe 10kwh a day in the cooler months? If you don't want to lose anything at all, move one string from the mppt to a second grid tie inverter.
Click to expand...
This is the key part of that:
feeder tap or supply side tap as the point of utility interconnection

So unless whole house, the limits are there.
 
Vince Mex said:
It is a whole house system. And the problem is that EG4 told me that the grid pass through is NOT working when the 18K is AC coupled with the generator port. Its internal relays has only 2 poles so it is GRID/GEN, GEN/LOAD or GRID/LOAD so you can not pull in extra power from the grid if your solar array is not enough because there is only these 3 modes....it seems to be either pulling all from the solar or all from the grid but not mixing bother in case the 18 k is AC coupled with the GEN Input. By the way is there any other solution to AC couple the 18K ?

I see only the Victron Quattro able to do so....but it is much more expensive, needs 2 units to get AC240V and also need add some solar charge controller for....18 kwh of panel so basically it doubles the cost or more...

I am ok to loose the possibility to inject to the grid and built the 18 kwh array system with the 18k inverter apart from the 9.75 kwh grid tie system.....BUT i do not know how to make them work in the same house without troubles.....

Sorry for my basic questions, i am no expert
Click to expand...
I am not seeing this happen with my setup.

When gen and grid are connected, the AC from the gen side, just feeds in with grid power. You are past the 200 amp breaker, and feeding to your load center. The 18 isn't inverting that power, unless it goes to batteries.

If there is excess, it goes back to grid.

I think the person you spoke to is misinformed.

Here is the state of my 18 as of a few minutes ago. Feeding the house, the batteries and pushing power back to the grid. Power coming from AC couple and PV.
3-26 18kpv.png

And second is a few minutes later, batteries full, and backfeeding from both AC Couple and PV.

3-26 18kpv 2.png
 
Well i am no expert and the person who wrote me this is an EG4 employee of the System Design Team so i trusted them.

You seems to have a similar system to the one i am building....and it seems to run just fine, if you are ok i will pm you for more details, thank you
 
millsan1 said:
It only works on the gen side
Click to expand...
Are you saying the Load side is not bidirectional and that is why it would not work when the grid is up? Or are you saying that when the grid is down the Gen port is the preferred way to ensure the inverter can cut off the AC coupled solar quickly? I do not know the particulars of the EG4 but those ports are typically bidirectional, at least that is the case with my SolArk.
 
Ampster said:
Are you saying the Load side is not bidirectional and that is why it would not work when the grid is up? Or are you saying that when the grid is down the Gen port is the preferred way to ensure the inverter can cut off the AC coupled solar quickly? I do not know the particulars of the EG4 but those ports are typically bidirectional, at least that is the case with my SolArk.
Click to expand...
When AC Coupled, the gen side is connected to grid when grid is up. When grid is down, the gen side gets connected to load.
 
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