Hi Guys, sorry I only just came across this discussion.
Keith, oversizing the solar PV is not the problem. I am almost certain it is a grid voltage issue which is causing your inverter to trip-off or shutdown. The Australian standard (AS4777) requires all solar inverters sold in Australia to ramp down (throttling) when the grid voltage rises above 253V and shut off completely above 255V. This is to try to keep the grid voltage from rising too high.
Unfortunately this now a common issue in area’s of high solar penetration (high percentage of houses with solar), but often only an issue in summer when solar generation is at it’s peak.
There’s are some ways to get around this such as by using a device called a ‘voltage optimiser’ which is designed to adjust the voltage in your home to be lower than the grid voltage thus allowing your inverter to still operate with high grid voltage. I would be careful though as some of these do not work correctly or are not certified for use in Australia.
Here’s a good article about the issues…
The best path to take (but more difficult) is to contact your local network distributor, which I believe is Ausgrid in your area, and tell them to lower the voltage at your local transformer (called re-tapping). No doubt this is a problem in the whole area and many people are simply unaware. Unfortunately Ausgrid will probably not listen to you unless you can give them evidence of high voltage in your street. Many modern inverters can log the grid voltage and if you have a wifi connection you might be able to get the data. Otherwise you may need a power meter installed or a device such ‘Solar Analytics’ energy meter.
Hope this helps,
Jason