Shelly em to monitor solar

I think im just not grasping how this works…
I have a small solar system mainly for emergencies but i do have transfer switch so i actually run a single circuit for tv off solar 24/7! VERY cool. incase of power outage i can turn on 6 circuits to home but thats for when grid is down.

Anyways i thought i would get this into HA as everything else in my home is but i must be missing how it caculates PV Production? I connected Shelly EM to output of my inverter that currently only runs a TV in kitchen and added this Shelly EM to home assistant under the energy solar production. How can this provide what i am producing? or can it only show what i am consuming? i did enter max Watts of PV is it all just math and estimations? or am i going about this completely wrong?