For Brisbane climate only. The later models of the Solar HWS with evacuated tubes have the pumps cutting off when the water temperature hits 70 degrees, I believe. Also what portion of the tank is 70 degrees ? The Flat panel solar HWS using thermosyphen principles and no pump just continuously heat up the water making the whole tank hotter.It never switches off until the sun disappears. Ignoring other considerations wouldn't this make the Flat Panel solar HWS better on most days in terms of the total volume of hot water heated. The whole tank, in theory is heated to the same temperature. In addition there is almost nothing to break down with flat panel systems , no controller electronics or pump Up until now I was strongly in favour of replacing my flat panel system with evacuated tube system. I would be really interested in a technical reply . I have never seen this discussed anywhere. BTW if in a Canadian climate I would jump on Evacuated tubes.