As I have a 3phase system installed here, I can provide you with some graphs or input.
Here is an overview of the voltage range on a cloudy day:
This is one of a sunny day:
To make matters worst, I have some friendly neighbours/solarpanel installers who ignore the Belgian voltage capping and often on sunny days I manage to measure 250V and beyond on one of my phases, causing high voltage spikes and drops which shutdown one of my PV systems.
I have 2 solar invertors, one connected to the 1st phase (green) and one connected to the 2nd phase (red). The panels are located on 2 sides of the house, facing east and west. Green is east, red = west.
All these values are measured on a seperate voltage transformer for each phase. I have 3 outlets installed near my electricity cabinet, one for each phase and thus connecting one adapter to one TX. I use some of the openenergy community i2c magic to couple the 3+1 TX boards together and send the data to my local emoncms installation. I really like your solution with the ESP; I was in the process of building a 3 x 12 CT board with an arduino due, but it got on the bench due to lack of time and I feel like it might be replaced by this nice piece of hardware.