My AIO2 and Gateway installation was in February. I had a pre-existing 3KW solar installation from FIT days. My installer says I don't need any certification of the work.
What I can find on the web suggests that I should have an EIC and must have a Buildings Regulations Compliance Certificate. He promised to apply for a G99 but I have not heard anything yet.
I would be very most grateful for clarification from someone who knows definitively what I should expect to get.
I have a 3.8kWh old FITS system (2011) and I had 2 x 6kWh AIO V1 installed and Gateway in 2025. My Installer had to apply for G99 before installing. My Installer commented that every time an inverter is added to a system the DNO need to know about it.
You need a G99 application when installing solar panels, battery storage, or other generation systems with a total inverter capacity exceeding 3.68kW per phase (or 16A). It is a requirement for DNO approval to connect larger, more powerful systems to the UK grid, often processed by installers
The items below are what I received from my Installer after Installation was complete
G99 Approval Letter from DNO and advice that Approval notified to Electricity Supplier
MCS Certificate for the Installation (required to apply for Export)
Electrical Installation Certificate and test results
NIC EIC Building Regulations Certificate of Compliance
Handover Pack Including Startup Shutdown Instructions and Schematics
Oh and I forgot to mention that in order for my Installer to be able to apply for the G99 on my behalf, I had to send an email in a specific (DNO approved format) to my installer authorising them to do so, Which was then forwarded to the DNO. Without this the DNO wouldn't talk to them about any third party applications.
I would check all of these things if I were you
RichardJ I agree with what @duplada has said, you need a G99 or G100 approval BEFORE installation of any additional inverters or battery storage. I had to have a G100 before my initial install and then a second G100 for a subsequent battery install.
If its a first install and its less than 4kW then the installer can do a G98 notification after installation, but in your case this doesn’t apply.
You need all the documents listed above.