I currently have 2kW of solar panels and a Sunsynk inverter (panels existed when I bought the house, the inverter is new).  After many months of waiting, I finally got my certificate in Feb this year to say the system is approved and all is good.  The installer who replace the inverter was the one who did the application for me.  He has since closed his business and gone to work for a much bigger company.

Now I wish to add another 3kW of solar panels, but I'm finding it difficult to figure out what is required to apply/register for this.  
I started filling out the CoCT solar application form, ticking the "Change to System", but realized by the end that nothing changes on the form.  Nowhere does the form ask for number of solar panels, wattage or voltage.  It only asks about the capabilities of the inverter.  I have all the documents the installer submitted for me previously, and it appears the only place the panels are listed is on the diagram.  I'm assuming then that I probably just submit an identical application and a different diagram?

I tried emailing the city department, but it's taken them 4 weeks to reply with a standard set of links about installing a new system.

Has anyone in Cape Town had any experience with how to deal with adding additional panels?

Don't waste your time. You are registered, that's all they want for now. Later they will start taxing you because you have panels, so the less they know the better I suppose.

The treatment you are receiving now should be an indication of their lack of interest.