> Without declaration, there is not only a risk of grid overload and regular shutdowns of inverters, but technicians are also exposed to real danger during their interventions. An undeclared installation can cause serious electrical risks if technicians do not have the necessary information to work safely.

https://www.brussels.be/how-report-solar-panels-brussels

I have no idea how serious these reasons actually are. It seems registration is free, though you do need to have a digital meter, which may incur extra costs. The system is apparently designed to encourage self-usage rather than feeding back to the grid.

I don't really know the benefit of not registering. To register you may need an inspection, which could be a pain and cost some money. But if you've spent a bunch of money on a system... why not do the seemingly small extra steps?

To fine them and make them pay continuous taxes of course!