LorenAmelang(Sorry I can't write in French...)
#SolarThermal has provided most of my hot water for 35 years. Lots of learning about #FreezeProtection at first - "drain back" required an unbearably noisy pump, "drain down" required tricky valves that failed often. And domestic water in the panels quickly clogged them with #HardWater minerals.
What works is a closed loop with antifreeze in the panels and a heat exchanger, heating a large storage tank. Domestic water passes through another exchanger in that big tank as it is used.
In my system a gas heater or a #WoodBoiler can also heat the big tank when there is no Sun. And the accumulated heat can be pumped through #Hydronic floors. All this was a huge expense at first, but divided by 35+ years (and current fuel prices) it is wonderful!