Have a look at Whirlpool Green Tech Forum. Generally, for an average household, the consensus seems to be that the best ROI is with a large solar PV system (5kW inverter, 5-6kW panels) & an electric hot water system.
SolarHW is quite expensive, but it's quite favorable in your location (further south it doesn't produce enough heat in winter). But in summer it still wastes excess energy, while solar PV can export that excess energy for a profit.
Heat pumps are also expensive, & reliability is an issue for some of the more poorly made brands. Heat pumps are extremely efficient, but if you have the unshaded roof area, your likely to get a much better ROI with a solar PV electric HW combo. If you have a small roof area, or some shading problems, then solar PV/heat pump may be an option, though it's an expensive initial outlay.
Just make sure your solar PV inverter had a relay that will heat your water before exporting excess electricity (Fronius is a very good inverter with this option).
ddarroch
Related Discussions
What could Australian homes learn from the rest of the world?
Q
Experience with Solar Heaters?
Q
Underfloor heating — worth the investment?
Q
Hydronic heating and cooling — worth the money?
Q