Is continuous circulation via solar panels, instead of on-off circulation (off when things get too hot) a valid design?
Yes. To control potential overheating, besides using “downstream” thermostatic blender valves say at the top of a cylinder in appropriate places such as at showers or at the top of the cylinder, solar thermal design niches can use several more “upstream” approaches. Old solar pansl usually use a solar controller to switch off the solar pump when the top of the solar hot water cylinder reaches a certain temperature, usually somewhere in the range of 65-85C. But, by not removing the heat the solar panel gets hotter and hotter, typically 150 plus C in full sun. This exposes all closed circuit solar panels to “solar stagnation” which brings very high temperatures and pressures, engineering and stress considerations which inevitably constrain the design of its solar absorber surface to being made of metals. High pressure stagnation also constrains the plumbing design to a system, which if it were ever to burst would release superheated steam. Another older option is to remove the pressure c
