Learn more about the battery management protection
With your battery set to charge first, there may still be times it will discharge a small amount of AC power back into the grid. This is due to the battery management system which is there to protect the battery from being damaged.
Part of that protection involves ensuring there is sufficient charging current during the charging cycle and preventing any excessive charge cycling at elevated levels of battery state of charge. For that reason, when there are only a few hundred watts of excess power from the solar PV system this will be exported to the grid rather than be stored in the battery.
Part of that protection involves ensuring there is sufficient charging current during the charging cycle and preventing any excessive charge cycling at elevated levels of battery state of charge. For that reason, when there are only a few hundred watts of excess power from the solar PV system this will be exported to the grid rather than be stored in the battery.
This also helps prolonging the life of the battery, so what you are seeing going back to the grid is perfectly normal and if it weren't to happen the battery would be in danger of becoming damaged.