Question: What will happen if I send some energy from my GridFree installation back to the grid?

Answer: Most likely nothing will happen. From technical point of view: your few watts are nothing in comparison with the mega and giga-watts that are handled by the utility companies. It is like throwing a pin over the border to a neighboring country.

From the financial point of view you need to note: you will pay (!) this energy as if you consumed this energy. As explained here, the majority of electric meters measure only the absolute flow of the energy: if you send the energy back to the grid, you will have to pay for each kWh the same price as if you took it from the grid. That is why it makes no sense to send the energy back to the grid. Save money buy consuming all of your own energy by yourself.

Note: from a legal point of view: in some countries it is not allowed to send any energy back to the grid without a special permit (license). In such locations we do not recommend to send any surplus of the energy to the grid.  Use the current monitoring relays and reverse current relays to block the overflows to the grid.