The answer is simply no. There is no need to inform your network operator, DNO(Distribution Network Operator), or the electricity supplier. There are different authorities that manage and maintain the electricity grid but none of them have ever enacted a policy for the off-grid system that generates electricity from the sun.
The main reason is that an inverter and solar MPPT charger that is certified as off-grid, is not made to export energy back to the utility. The DNO will never experience any disturbances from your solar installation, it will not affect the public network and more importantly in the emergency of a power cut, it is safe for the maintenance engineers to carry out any repairs without any risk of unwanted electricity flowing backward.
It is fair to consider that the off-grid inverter is acting in a similar way to an EV charger, which takes energy from the grid. The installation of EV chargers does not require a special license either.
It is great to be power independent, but we have to follow some important electrical rules :
You can watch online one of our off-grid systems that electrifies an entire property with 2 8kW Conversol Max inverters