For a working family, if you have 1 kilowatt of solar per person then most of the power will be used in the day and very little exported to the grid at a low feed-in price. You can add another bank of solar panels but a higher proportion of this power will be exported at a lower price and so it will take longer to pay for itself.
For a retired couple or for family with children not yet at school, you can get a better return on more solar because more power is used in the day time.
For a family with teenage children, more power is used at night. Now the economics are more favourable to extra solar with battery storage so that power that would have been exported at a low price is instead stored and used when you need it most.
Look at your power bills and work out how many kilowatt hours you are using per day. For NSW, divide this number by 4 to get the kilowatts of solar you would need to supply all your needs for an average day. The amount of power you use at night will determine roughly how much of the solar power would be exported if you have no batteries.
The above is just a rough guide. Air conditioners, pool pumps and other power hungry devices change the picture. If you have teenage daughters you should have solar hot water already. Extra solar or batteries will pay for itself but how long it takes will depend on feed in prices and how much power you use at night.
Note: Presentation at Murwillumbah World Environment Day – the file is too large to for this web licence. Please request by e-mail.