Metering technology used in Rooftop solar system
In general there are two types of meters: the export or sell meter, which measures the electricity fed into the grid, and the import or purchase meter, which measures the electricity drawn from the grid.
In the case of net metering, the owner consumes the power generated from the solar PV system, and when the system generates more power than the owner consumes, the excess power goes to the utility grid and the meter might run backwards. Thus the domestic electricity meter has to be changed to an electronic meter with a reverse running function that can record both power going to and power coming from the utility grid. These two readings are used to calculate the electricity bill.
Meters also are needed to measure the generated power of the solar PV system, the electrical power drawn from the utility, and the power supplied from the solar system to the grid. A system configuration under a feed-in scheme as shown below
Smart meters record the consumption of electrical energy at intervals of up to 15 minutes and communicate this information to the utility for both billing and monitoring. Such meters can include other functions, such as remote disconnection of the solar PV system and integrated radio communications.