A. In general, a 6.6kw system would suffice for electricity bills up to about $750 per quarter; for bills between $750 and $1200 per quarter, seek for between 6.6kw and 10kw; and for rates beyond $1200 per quarter, search for a 10kw to 12kw system.
The best return on your investment is to be able to use your solar power yourself while it is being generated, as this covers the full cost of electricity you would have had to purchase. If you are not home to utilize the power, your excess power will be sold to the grid at an agreed-upon price by your electricity provider (OriginEenergy, AGL, Red Energy, etc.). The selling price is always lower than the price you paid for your power.