My father-in-laws system has a control centre pump and valves and a hot coil in the immersion heater lower down to the original hot coil. There are two panels one east and one west and two sensors on top of panels, plus a sensor on the hot coil, idea is if sensor on panel detects more heat than sensor on hot coil the valve opens and pump runs on that panel.
They removed the immersion heater when solar panels were fitted, so when the central heating is not running it is the only way to heat water, the central heating has failed a few times, each time no hot water was the result.
My brother-in-law had electric solar panels fitted, and when he was not using the power they produced it would pump the power into an immersion heater rather than into the grid, this actually worked, however the control system was really complex.
He had two huge tanks, very well insulated with hot coils already installed, each method of producing heat would feed into these tanks, LPG gas boiler, wood burner, and solar panels, and the central heating pumped water out of the tanks around the house, domestic hot water was a hot coil in top of tank. There was a temperature gauge by the wood burner marked to show if the tanks had the capacity for a burn.
The problem with a wood burner is to work efficiently it has to run at a set rate until all wood is turned into charcoal, otherwise you get either particular emissions or tar build up on the flue, since you don't want same output every day, the only way to use a wood burner or coal burner for that matter is to store the energy either in stones or bricks around the fire or in water. Water lends its self to being controlled better.
In his case he hardly ever used the LPG boiler, and it needed to be fired up manually if required, and would then shut off once the tank was at around 60°C allowing space for other heating options. After his wife died he did not spend so long at home, and the temperature would be set at around 12°C to stop anything freezing, however there was a safety radiator which would auto switch on to cool the heat store if it got too hot, this was it seems often hot when he got home and even in winter house never cooled below around 15°C as a result.
He has now moved, wish I had taken more notice of his system, however I understand on the building of the house the heating system cost around £24k so it will take decades to pay for its self, it would seem the builder made a loss on the house, originally built for the builders family, now with its third owner, built around 2000.
What was interesting was how much wood my brother-in-law used, it was around a 1/8 of the wood used by a friend of mine with a 20 acre woodland, in spite of house being 4 times the size of the woodland dweller.
However back to thread, it would seem only way to heat water using sun light is to use electric solar panels and an immersion heater. At least in the UK, daughter has property in Turkey and there water filled solar panels work well, but not in the UK.