Hello Marty,
There has been a lot of bad history concerning heat pump technology in Victoria, and to be honest a lot of people have the misconception that it is technology that wont work for us in the southern states.
Perhaps the biggest contributor to this ideology is the Heat Pump scheme that went in a few years where thousands of those “Quantum” Heat Pumps were installed across the state, and failed to deliver the savings promised.
Quality Heat Pumps are incredibly efficient, there are studies and tests that actually show them being more efficient than actual Solar Hot Water Systems. Units such as SANDEN and Stiebel Eltron have units that will use less than 3kWh per day to heat 300L of Water around say Sydneys Latitude, but having said that, they are still very efficient down here(Victoria).
We actually install them nowadays in Off Grid Situations as we are that happy with there performance. You can get Units which have an electric element Backup, but with the top end units having sub-zero operating temperatures as low as minus 5 and the ability to program them to run in the middle of the Day when you are producing Excess Solar Power and the ambient air is a lot warmer, they are extremely efficient.
The only downside really, is the fact there is more to breakdown, but if you buy quality you get quality and the service on the top end units is great.
All in all, they are a great unit to use for Hot Water Heating, Especially as an accompaniment to a good quality Solar System.