With low solar panel prices & moderate priced Renewable Energy Certificates (RECs), buying extra panels for your new stand alone power system makes a lot of sense!
For instance, 8 × 185 Watt Trina solar panels $830 = $6640 RECs $36 = $5508, so about 83% of the PV cost is subsidised!*
If your system is over 1500 Watts, it will need to either a) cost more than $30,000 to connect to the grid or b) you are situated more than 1km from the grid to get 5 for 1 solar credits (for the amount over 1500 W). The system must be new (not an add on) and it must be installed by an accredited solar installer. There is no rebate for other materials, eg batteries, inverters, mounting frames.
With a larger PV array, you can arguably spend less on batteries, the batteries will keep better charged up and in sunny weather you can probably do a bit of cooking (if your inverter capacity is large enough).
*Prices correct at time of publishing.