The sun’s rays hit the solar panel and transfer the thermal energy to the panel’s copper surface (the absorber); this heat is then transferred to the ﬂuid (a mixture of distilled water and glycol) running inside the copper tubes which in turn heats the domestic water inside the boiler.
There are 2 different ﬂuid circulating systems:
a. Natural circulation; when heated, the ﬂuid becomes less dense and lighter and ascends towards to top of the collector into the closed circuit chamber in the boiler. Once inside the boiler’s closed circuit, the heat is transferred into the sanitary water you use in your home; during this process (ceding thermal energy into the sanitary water), the ﬂuid becomes colder and denser and therefore descends to the bottom of the closed circuit chamber in the boiler channeling it to the bottom of the collector. At this point the process restarts; there is no need for any pump as long as the boiler is located above the panel/s. This process runs by itself generated by the heat of the sun;
b. Forced circulation: instead of the ﬂuid flowing by itself following the laws of thermodynamics, the ﬂuid is forced through the panels and the closed circuit by a small electric pump. An electronic control system ensures that the fluid circulates keeping the temperature in the panel is higher than that in the boiler. Forced circulation is used when the boiler is installed below the panel/s.