DNO types explained

DNO applications are needed when installing solar PV panels, battery storage where the battery has a back up or “islanding” functionality, heat pumps, and EV chargers.

You MUST apply for the DNO before installing your system.

There are basically 3 types of DNO for solar PV:
G98 – for systems if the generation is more than 16A per phase which is the equivalent of 3.68kW for a single phase supply or 11.04kW for a three phase supply.
G99 -for larger systems up to 50kW or systems if the generation is more than 16A per phase

G100 - if your G99 application comes back and your system’s export needs to be limited, a G100 application is required.

Your installer should undertake the DNO application for you.

When fitting solar panel installations in the UK, G98, G99 and G100 refer to engineering recommendation documents issued by the UK electricity regulator, Ofgem. These documents outline the technical requirements and standards that must be followed when connecting small-scale renewable energy systems, such as solar panels, to the grid.

1. G98: Engineering Recommendation G98 (ER G98) applies to solar panel installations with a capacity of up to and including 16 amps per phase (or 3.68 kW per phase) and are intended for domestic or small-scale commercial use. G98 is known as a "“connect and notify” notice. It sets out the requirements for connecting these installations to the low-voltage (LV) distribution network. Installations complying with G98 do not require explicit permission from the Distribution Network Operator (DNO) but must adhere to the specified technical standards.

2. G99: Engineering Recommendation G99 (ER G99) is “apply to connect”and applies to larger and more complex solar panel installations with a capacity exceeding 16 amps per phase. This could include commercial-scale installations, multiple installations, or installations with energy storage. G99 covers a wider range of technical requirements, including protection, control, and monitoring capabilities, to ensure the safe and stable operation of the grid when connected to these higher-capacity systems. G99 compliance requires explicit permission from the DNO, and the installation must go through a formal application and approval process. Depending on the network operator the process can take between 8 and 12 weeks, and in some cases as long as 4 months!

3. G100: If your G99 application comes back and your system’s export needs to be limited, a G100 application is required. At Innocent Energy around 12% of our solar PV DNOs get limited. Applying for a G100 DNO will cost an additional £300-£700 for the application, and also increase your lead and installation time, as an extra device will need to be installed along with your system.

G98, G99 and G100 aim to maintain the stability and integrity of the electricity grid while allowing for the integration of renewable energy sources. They outline standards for safety, anti-islanding protection, grid protection, and connection requirements to ensure that solar panel installations do not adversely affect the grid or compromise the safety of workers during maintenance or repairs.

It's crucial to consult the specific guidelines and requirements outlined in G98, G99, or G100 depending on the capacity of the solar panel system you are installing, to ensure compliance with the regulations set by Ofgem and the DNO responsible for your area.