You must notify the relevant DNO of your electricity generating installations in all instances, including Solar PV technologies. Depending on the capacity of the installation, the DNO can either be notified of the installation after it is commissioned, or there are scenarios where prior permission must be granted before installing.
If Engineering Recommendation G98 applies to the installation and the size of the Solar PV installation is under 16 amps per phase, the DNO will need to be notified within 28 days of the system being commissioned. You will need to complete the following installation document: G98 Form B Single installation of microgenerator
If Engineering Recommendation G99 applies to the installation, and the size of the Solar PV installation is greater than 16 amps per phase, then prior permission to connect will need to be granted. As the scope of MCS certification for electricity generation is a maximum of 50kW, Type A G99 is required to be completed for higher capacity MCS installations. You are required to complete the following form in this instance: G99 Form A3-1 Installation of type A power generating modules
More information on notifying DNOs is available in the Distributed Generators Connection Guide: https://www.energynetworks.org/assets/images/Resource%20library/G99%20Type%20A%20Final%202020.pdf