The following is a really useful calculator that allows an estimate of savings of simple solar PV systems and upgraded systems with battery storage.
I ran our data through it for a 5kW system in SE Qld.
The calculator forecast 7637kWh of annual PV generation. Our rolling average after 16 months 7630kWh. That is our actual inverter data!
A $5,500 investment in solar PV generates cumulative savings over 10 years of $17,708.
With an added Tesla PW2 the investment required increased 4 fold to $20,850. The cumulative savings over 10 years $20,083.
For a simple PV system the net savings over ten years assuming a personal loan for the purchase at 12.5% variable interest will be approx $10,000.
For the upgraded battery option the net savings over ten years are effectively zero. There are plenty of loan calculators around for those who like to practice accounting skills.
Finance options for Battery System
The interest ($2,500 pa ) is greater than the savings if the Powerwall 2 option is financed with a personal loan. No go!
For homeowners with a redraw on the home loan, (approx 30% of Aussie households) there will be a residual of approx $7,000 owing after ten years. That is if all the savings in electricity bills go to repaying the extra borrowings. Alternately allowing the debt on the home to balloon would increase. The total debt on the system to more than $35,000 owing after ten years.
Alternately if you have a spare $21,000 in cash spending it on a solarPV + battery system will give you back approx $21,000 over the ten years. A very similar return to the current zero% bank cash rates.
Or a Special case for those with a spare $20k in cash.
A better outcome using just $5,500 to buy only a solarPV. That would leave more than $15,000 up front to invest as needed. You could even add that into super if you are eligible. Plus a further averaged $1,800 per year of genuine savings including up to $300 in real cash credits to add to your investments. One great way to save for that new battery electric car. Just don’t let P Dutton find out you are going to pay with cash. 
(Edit)
P.s. Just finished reading the updated battery test progress report. Hope they more funding in the future to continue testing new products as they become available.
