Net metering is a system where the amount of energy you buy in from the grid and the amount of excess solar energy you export to the grid are recorded separately and you are only billed for the net of these two numbers. So if you import 1000 units of electricity over a month at times when your solar is either not generating (night time) or not generating enough energy to cover all of your needs (say a cloudy day), but you export 500 units of energy to the grid in the same month at other times when your solar is producing more energy than your house/facility is using, then you would be billed for only 500 kWh.
Example: If you receive electricity from a grid it will run in forward direction and when excess solar unit is supplied to grid then it will run in reverse direction. Suppose you import 100units/month and export 80units/month, then you have to pay for 20 units only. Incase solar units supplied to grid is 120 units/month then KEB will pay you for that excess 20 units and it will be cleared at the end of month and no carry forward to next month.