Gavin is right. I set the parameters in PVSol to -28C for the very reasons he states. I have seen this as a night time temperature in the Highlands. The cold sucks the moisture out of the air. When the sun comes over the horizon and hits the very cold but frost free panels, the voltage can rocket.
As for Oz, sounds like Queensland - lovely at this time of year. Calc is going to be different due to ambient temperature and much higher irradiance. 3.5k could be likely. Most inverter manufacturers have web based design tools. I would run it through that using local climate data if you do not have access to something like PVSol.
With the rest of this a trip to blighty may be in order. Great training available.
I am sure Andy from Sibert or other supporting supplier on here would be happy to export some top notch balance of system items to you to help overcome some of the challenges you are facing.
As soon as you touch adapters system starts working.
