timmmay:

 

Thanks all. It sounds like a midsize solar system would significantly reduce our bills and a payback would be less than 10 years. I guess it's a toss-up between paying high electricity bills and keeping money invested, or reducing bills. 

 

I guess those two prices are plus installation?

My advice would be to get the largest system you can afford and fit on your roof. 

Those prices appear to include installation.

I assume you're aware of the low interest loan offers from the banks for solar. This is a good way to get cheap money. Even if you already have the money to pay upfront for a system, you're better off keeping that in the bank and getting a loan at 1% if you have the option. This alone will add to your returns.

 Is there any advice around whether a battery is worthwhile? Obviously it lets us time shift our power which has big benefits. In the winter even though we preheat the house during the day we have a lot of usage in the evening. I wonder if the ducted heat pump would use the battery fairly quickly and cycle it every night, meaning the battery probably wouldn't last all that long.

That very much depends on your usage patterns and ability to self-consume the solar you will generate without a battery. The fact is most houses don't use a lot of power between 10am-4pm which is when you're generating the most solar energy; this likely isn't a time when you need a lot of heating, do a lot of cooking, or use a lot of hot water. Hot water can be timeshifted with a diverter and treated as its own kind of energy storage, but for other applications a battery is the way to go. A battery also gives you more scope to take advantage of time-of-day differential pricing plans.

I'm not sure about other brands, but Powerwall batteries are warrantied for 70% capacity after 10 years. Real world, people are seeing ~1% reduction per year with daily cycles. The battery should have long paid for itself before you need to think about replacing it.