the excess power from first system would be available to the second system to charge the batteries and those 8 panels might produce more than I use and upload the excess if the batteries are full.
OK, in this case you would need to run CTs all the way to your main panel to monitor the excess export from your Enphase. Do you know if the 18kpv is intended to be wired up with analog signal to CTs and/or with digital signals to a Power/energy meter, which then does the CT readings and digitizes it?
Have you confirmed that the CTs will fit in your main panel? Some of them are arranged in an incompatible way, and there is no way to modify (IE, if there is no access even for ribbon style CTs to go in).
Nit: upload -> backfeed
I plan to be on batteries from 4-9pm and also upload to the grid during that time.
California? If so you will need to update your interconnect agreement to include ESS. And as precondition of that you will need a permit application; the plans will need to show backfeed calculations.
the 18kpv is connected to a 50amp breaker on the other bus bar, it's a 100amp sub panel with 6-8 circuits with low usage that averages 24kwh daily. sub panel is about 30ft from main panel. my biggest question is it ok to have power feeding back to the grid from two sources?
Can you spam photos of your panels, etc, that will bypass some drip feeding of info? Also TBH I feel this approach to adjusting your design is kind of backwards.
What is the breaker size on the Enphase? What is the main breaker size on main panel?
My guess is you are in trouble on both panels and need to do some refactoring.
Subpanel with 18kpv. Low usage on subpanel is irrelevant to code, code cares about whether the busbars have enough capacity.
120% rule (not the only 705.12 calculation but we can start here) says backfeed + main breaker on subpanel needs to be < 1.2 * busbar capacity.
You are supposed to put the 18kpv (or any other solar inverter output) on a breaker that is 125% of the AC nameplate. OR lock the max AC output below 80% of the breaker. So your 50A breaker here is wrong. 65A seems right to me (feel free to check the manual or ask EG4 support whether 60A or 65A is OK). That means your breaker for feeder to subpanel should be 120 - 65 =
55A. On the systems I've designed so far for myself, I had to install breaker on both sides of the feeder to each subpanel with backfeed. So your subpanel here needs to have a main breaker, most likely a backfed main breaker.
Note: I believe 120% rule actually refers to ampacity of the inverter output, not the backfeed breaker size. I don't think this subtlety changes the conclusions. It'll give +/- 5-10A difference in answers
Main breaker
You are probably also in trouble
30 ft is probably OK for analog CTs, I would recommend asking around here though for confirmation from someone who has installed this config.
Let's say you have two full 20A branches of Enphase micros. 1.2 * 200 - 40 = 200A main breaker.
You need at least 60A breaker for your 18kpv. Which means your main breaker would need to go down to the largest size <= 140A. This may end up being painful for your house's load calculations.
You may also run into trouble with your AHJ on the definition of "feeding the busbar from the other end". Are the Enphase micros backfeeding through an Enphase combiner box? If so then this is less of an issue b/c there would still be another pair of breaker slots on the bottom.
Alternatives
Alternatively you can avail of the 200A transfer relay on the 18kpv and hook it in upstream of your main panel. You're paying a premium for this capability as a user of 18kpv
