Hi @mkgregg
You'll need to know somehow what you are producing, something independent like the solar system software.
Most modern systems have this as standard
Do you have any sort of app that shows splits of what you use and what you send to the grid ?
Eg . . . mine today so far is 12.6kw, with 40% to the home, and 60% to the grid.
Hopefully you can access such info on an app, otherwise you are sort of blind.
With an analogue meter, I'm not sure you can work it out at any one point, apart from bill time when you can take all your app info on production total (eg the 92 days for the above bill), and compare to the 92 days or whatever it is on the bill.
There should be the difference showing what you produced and used during the day.
For interest, deduct that from the total, and see what your solar feed is on the bill, it should be close, and what's left out is what your system losses are (running inverter etc).