Incorrect data

Data for my system - either via the app or online are incorrect - by some margin. for example 3000KW generated in a day exported nearly 5000KW !!

Is it just me and in which case how on earth do I fix ?

If you have an Android device (ideally a tablet) try this app

https://play.google.com/store/apps/details?id=uk.rubikcube.invertermonitor

Turn on the collect stats option and just leave it running.

LMA It would probably help if you provided some details of your system and settings.