I’ve never had solar but don’t you have to let the electric company know so they can setup the net metering? If so they would know that is in the mix.
They use old fashioned mechanical meters here, not electronic smart meters like the States converted to years ago.
When it comes time to read the meter, they have a kid go around with a handheld computer and of this portable thermal printers like you may have seen at a rental car check-in point. He prints the bill out and sticks it in your mailbox. When he gets back to the office after doing his rounds for the day, he plugs the computer into the network and uploads ask the fresh meter readings...you can pay the bill online immediately after he uploads it.
If the current flows into the grid from solar instead of out of the grid into your premise, the meter runs backwards. As long as they can bill you for a few kilowatts a month, nobody asks questions. Electricity here in my province is about 1.3¢ per kilowatt hour, so making sure that they can bill 20 or 30 kWh per month is no major expense.
And that's where this kid in Nakhon Ratchasima screwed up. Had he let them bill him for a few kilowatts a month, nobody would've ever caught him.