One meter, two 200A main panels, EG4 18KVP, CT sensors, zero-export

[averagejoe13]

I am looking for a solution to "supplement" whole house from EG4 18KVP. I.e. idea is to have EG4 18KVP inverter produce no more than house is using (for now, without batteries, in future I likely to add these). I.e. zero-export. At the same time to have grid power available when sun is out or when HVAC compressor turns on.

I do have two main panels, each with its own 200A breaker. I want to feed house load through a double pole breaker in each main panels. There is little to no space to put inverter between meter and a panel. And redoing that part is tricky due to how wires enter ting the meter and wires entering the house.

My understanding is that it is possible to splice in second pair of CT sensors to measure L1/L2 combined in both panels.

I will start with a tiny PV array of 10 250W panels, with intention to start small and add PV panels overtime (I have plenty of ground space)

(I am new to all of this, just reading a ton for now) Questions -

1) Is adding/splicing-in another set of CT sensors is reasonable idea? Any concerns I should have besides sourcing right spec ones?
2) Is feeding both panels from the same inverter at the same time can cause issues?
3) How I should calculate proper double-pole breakers amps for use inside each main panel? Should it be 50A for each or 25A for each or 120% of 50A/25A? I am unlikely to have both panels maxing out EG4 18KVP spec'ed AC output at the same time, but each panel can draw close to that at different time of the day/year. (One panel has all HVAC stuff on it, second one have pool heater/pump/etc).

 

[Stephen InGeorgia]

I have no experience with this, but I've got the same issue with 2x200A panels. I don't think you can feed two panels with the same output (could be a little out of phase = boom). You could use the generator input/output as a dump load to the second panel, but you had better be net metered with the utility. If panel 1 fed back to the meter, then thru the common connection to panel 2, I think the CT readings would be all messed up.
When I upgrade from my two Sunnyboy 5kw, I'll get the EG4 or a SolArk and hook it just into panel 1 with all my vital 120v loads, then use the second panel with all the hvac and water heaters as a dump load during the day. Goal for me is to take the panel 1 zero export, and provide backup.

 

[ricardocello]

My understanding is that it is possible to splice in second pair of CT sensors to measure L1/L2 combined in both panels.

This is complicated.

I also have 2x 200A main panels fed from a 400A meter (actually 320A, but who’s counting).
I’ve got an ESS setup on one main panels with CTs, with critical load panels being powered by the inverters.
The other half of the house (up until recently) was a load I could not measure, nor provide power from the ESS.

So I’ve now got two EM530 energy meters with 5A CTs to read both 200A panels, and I’ve got them on Ethernet.
So in principle, the CT information is available to do whole house zero-export.
Without going into great detail, the only way to make this arrangement work is lots of custom software.

 

[ricardocello]

How I should calculate proper double-pole breakers amps for use inside each main panel?

will these breakers have physical interlocks up to code to ensure that grid power and inverter power will not mix?

 

[ricardocello]

If panel 1 fed back to the meter, then thru the common connection to panel 2, I think the CT readings would be all messed up

that’s my situation, but you have to add both meters power together (negative number + positive number = net power from grid)
And make sure the energy meter or AIO with CTs knows how to do that. no idea how to do that on an eg4 18kvp

 

[SunDave]

How I should calculate proper double-pole breakers amps for use inside each main panel?

will these breakers have physical interlocks up to code to ensure that grid power and inverter power will not mix?

Hi, Just a heads up. Along these lines. Watch out for issues with the neutrals as well. Especially if fed from two different meters. This seems complex. I would suggest:
a: Keep it simple
or
b: Get a skilled electrician involved.

Just one guy's opinion.

 

[wheisenburg]

What you are proposing here, is to put the Grid connection of your inverter onto both panels. If you connect your inverter to both panels, and the main breaker trips on one of the panels, you will have the grid connected to one panel, but not the other. If your inverter is hooked to both panels, your inverter will suddenly be trying to power the entire load. You definitely only want your inverter connected to ONE panel.

However since both of these panels are in front of the same meter, you should be able to do this by just figuring out your net consumption from both meters and then adjusting your export to zero the next consumption out. These panels are already tied together in front of the meter. Any power you put onto one panel will just flow through that connection to the other panel. But yes, you will likely need to hack your own solution to do that.

Is it possible to put your CTs on the common conductors that are between the meter and the two panels?

The other thing is, that unless you can place your inverter between the meter and at least one panel, you will not have back up power. You can feed power into the system and attempt to do self consumption, but unless your load panel is electrically moved to the load side of the inverter, you can't run it in a power outage.

 

[averagejoe13]

What you are proposing here, is to put the Grid connection of your inverter onto both panels. If you connect your inverter to both panels, and the main breaker trips on one of the panels, you will have the grid connected to one panel, but not the other. If your inverter is hooked to both panels, your inverter will suddenly be trying to power the entire load. You definitely only want your inverter connected to ONE panel.

However since both of these panels are in front of the same meter, you should be able to do this by just figuring out your net consumption from both meters and then adjusting your export to zero the next consumption out. These panels are already tied together in front of the meter. Any power you put onto one panel will just flow through that connection to the other panel. But yes, you will likely need to hack your own solution to do that.

Is it possible to put your CTs on the common conductors that are between the meter and the two panels?

The other thing is, that unless you can place your inverter between the meter and at least one panel, you will not have back up power. You can feed power into the system and attempt to do self consumption, but unless your load panel is electrically moved to the load side of the inverter, you can't run it in a power outage.

There is no accessible to me way to put CTs before both panel unfortunately. Meter is in the sealed box, and from meter box two conduits go to the left and right. And in about 8" or so are main panels.

I do have interlocked generator input on one of the panels - one that feeds most of the house. It is currently full. I was thinking about removing generator input and put inverter input in there if I would end up feeding both panels in parallel. But now I think the best way will be to feed it into the second panel only. In normal mode, like you said, current will flow to the first panel anyway. And in the case of blackout I still can use generator using interlocked breaker on the first panel to power the house without inverter being involved. I rarely have to fire generator up anyway.

I ended up buying Sol-Ark 12k. But I think it will be pretty much the same as EG4 18k wiring-wise.