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FormulaNova said..
I hate to contradict Macro (again), but the difference between flat-plate and evacuated tubes is minimal. Its the pumped setup that loses energy and can be very dependent on the length of the run of pipes.
If you have a roof mounted tank, thermosiphon, the same as the example, then they are about the same.
A pumped system will use electricity from the pumps obviously, but I would be amazed if it was even close to the energy used to directly heat up water with an element.
The pumped system offered here in Australia is open one at ground level.
Two circulation pumps, connected in serial , running at top power settings to pump in water onto roof of two storey building.
The water warm up ( or not) and flow down ) with gravity. Then need to be pumped ( not circulate) again 10 meters up. Obviously my first thought was to modify the system by installing piece of copper pipe, to convert open pressure system into heat exchanger.
To keep the pressure of returning from roof water at the pressure equal to the height.
This way single pump running at lower setting will be enough to push water resistance in pipes only, to circulate.
Not pump against gravity. All is needed is small cistern on top to regulate , refill circulation water . Like in all vehicles with water cooling engine system .
E-mgh energy saved
But such modifications of plumbing system by end users are illegal in Australia.Obviously Australian water system manufacturer could do the same in first place, but for some reason they don't.
For me not using sun to heat water for domestic use at home in Australia should be called crime and prohibited by law!
Good news is that I could now use freshly installed solar PV to power those pumps.
The bad news is that water heater element will switch ON mostly at evening , night after showers. That need to draw power from the grid, when energy prices is highest.Timer switch could solve the problem by delaying reheat till next day.
Next modification needed ? where are all geniuses designing our systems in Australia?