Planning for the future - String inverters > Hybrid

[Stephen InGeorgia]

I have a 13Kw solar array feeding two, 5.0 SunnyBoy grid-tied inverters. Each inverter has 3 MPPT inputs. Two inputs are strings of 8, 325W panels and one string of 4, 345w panels. Each inverter feeds an electrical panel (I have 2, 200amp panels). The two panels are tied to the same electrical meter the electric company uses to count instantaneous power in/out for my billing.

In planning for the future and adding battery backup for one of my electrical panels, I think I need to replace the SunnyBoy feeding that panel with a hybrid inverter.
The priority is to charge the battery during the day and use it during the night.
The second priority is to minimize the selling of power to the electric company.

I'm fine if I need to open the main 200A breaker and restart a hybrid inverter for a loss of grid situation (if that's possible to Island at the main panel)
I also have the option of AC coupling a hybrid inverter that will frequency shift the existing 5.0 SunnyBoy if I isolate the electrical panel.

Opinions on either setup?
How does a modern inverter limit selling power to the electric company? I'm fuzzy on how a current transformer works to identify power coming in vs. going out.

 

[DThames]

I am getting ready to install a couple of Sol-Ark, one 12k and one 15k for two different friends. In the setup software you can configure them to limit sell back or not sell back at all. This is fairly common with higher end hybrids, I believe. Youtube videos hosted by the manufacturers are helpful to understand features.

A current transformer (CT) outputs a voltage range that can be correlated to the current in the wire that the current transformer is around. The voltage is read by a computer. If you have a pair of CTs on your feed to the meter and a pair of CTs on your inverter output, the mathematical difference is the excess that you are making or the shortage that you are pulling from the grid. The direction that the CT is facing is important for this math to work. Normally the CT has a mark for direction or the software has a toggle to flip them around in the computer's world. I have a Sense home monitor with the solar option. They do all of their CT orientation in software. I shut down my main breaker once and when power was back on, my Sense was out of its mind, having flipped the solar to make it look like my solar production was actually a house load. Tech Support flipped it back and locked it in the software. Anyway, interesting on how they manage that.