Solar PV cells for households are a rort - big subsidy from taxpayers to assuage the green vote.

If it is a rort then who should be in on it? Probably all the fine members of this forum.
Best way to decide? As an investment decision, outlay now, income later.
The income has 2 parts:
1. the saving on the power you would otherwise have to buy,
2. the sales to the elec company from your PV system over the amount you use.
The outlay you estimate from quotes on the size of system you get.
Note- you do not get energy independence as if the mains go off your generation goes off as well (unless you get an extra very expensive option).
What you need to know:
How long it will last, the equipment may have a 20 year warranty, but what about the company? The buy-back tariff is for 10 years.
How much do you save? A 1kW nominal system will generate about 1600 kWh a year in Perth. Your installer, Luke or who you ask, should quote you a figure based on shade, angle, roof slope, technology... The normal tariff is ~21c per kWh so the saving for a 1kW system is (21c x 1600) $336 a year - but - if you use no power during the day, and sell all generated power back to Synergy at 47c per kWh, then the max income is (47c x 1600) $752 a year.
So for a 1kWh system, your annual income is from $336 to $752. At the low end if you are in all day, home office, aircon and big frigs. If you are out all daylight hours 7 days a week then you sell all your power at the high buy-back rate.
(For my house, aircon, home office, I sell back about 30% of the 1600 at 47c per kWh, and save 70% of the 1600 at 21c per kWh. I bought mine 2 years ago but since then prices have dropped and there is the new buy-back tariff, if buying now I would go for the biggest size that gets the subsidy - about 4 or 5 KW, depends on your roof area and direction of course).
Anyone who would like to see a little spreadsheet of the financial evaluation, send me a PM with an email address and I'll send it to you - fully guaranteed up to what you pay for it!