Solar water heating, especially in Australia, makes so much sense. I would say its a no-brainer, but some might baulk at that.
This DIY project took me all of two hours to complete. It is made from two lengths of 12mm polyethylene irrigation pipe, at a cost of about $50, a recycled galvanised disc with a steel frame, cost $0, and three lengths of recycles 25 x 25 x 2.5 aluminium channel , cost $0
I like the way it looks and it has heated our hot water on all but the coldest overcast days in the bush, and provided almost limitless showers for us and guests for many years.
Being a disc, its easy to reposition to take full advantage of the sun, or to avoid full sun in summer when the output is close to boiling.
The hot water gradually cools from really hot to warm over about 20 minutes, time for 3 or 4 showers, and reheats again in about the same time.
The capacity of the system is about 1cc per cm, or 1 Litre per 10 Metres of tubing. I guess it could be called an invention, its more of a rearrangement to me. The water adds about 20Kg to the weight, and helps it avoid being blow away in high winds. I tie it onto a tall fence pole for safety
The nice thing is it works so well!