You require an import/export meter which your power company will provide for you. This counts the amount of power that you import/export. The exported power is credited to you on your power-bill. In New Zealand, this is the ‘on-grid’ compliance requirements. We do not design the system for you to be making money off your panels by exporting back to the grid, but you will naturally feed power back to the grid if you have excess (think long summer days where you are at the beach and your house is powered and your battery is full – excess has to go somewhere!)