Do you need to install an additional electricity meter after the system has been installed?
Traditionally customers have only bought power from the supply company. The old meter only reads the total electricity consumed. (It does not even know that electricity can be generated in a home and sold to the grid, nor does know the terms ‘import’ and ‘export’ of electricity). Unless you have had your meter recently installed, your elderly meter needs to be respectfully retired, or at least, supplemented with a younger one which can record export of electricity. Basically you need a system which can record two way flow of electricity. This needs either s ‘smart’ meter, or two meters. The situation is complicated by the use of different PV incentives in different countries, and even different states within the US.
For example, in Australia, you are required by law to have a smart meter. There are two metering scheme in vogue, i.e., net metering, and gross metering. The smart meter does the function of two meters. It is a bidirectional meter. It can record the net electricity imported by your household, and it can be set to record gross electricity imported and gross electricity exported. The tariff schemes are different in each case. In net metering you pay for the net amount of electricity you import. Gross metering will be needed for regions using feed-in tariffs, or certain government incentives for production of alternate energy.
Most of the US states use net metering by law, but feed-in tariff schemes also apply. In each case, as a general rule, you will either need to replace the meter, or add another one.
The same is true for Germany and most of Europe. But the best advice is to consult the local utility company about whether, or how much they will buy from you and what sort of metering arrangements are necessary.