The sun rays hit the solar collector (solar panel) and transfer the thermal energy to the panel’s copper surface (the absorber), usually black or blue; this heat transfers to the fluid (mixture of distilled water and glycol) running inside the copper tubes which in turns heats the domestic water inside the boiler. There are 2 different fluid circulating systems:

a. Natural circulation: by getting warmer the fluid becomes less dense and lighter and naturally tends to ascend towards to top of the collector where it is conveyed inside the closed circuit chamber in the boiler. Once inside the boiler’s closed circuit, the heat is naturally transferred to the sanitary water you use in your home; during this process (ceding thermal energy to the sanitary water) the fluid becomes colder and denser naturally starting descending at the bottom of the closed circuit chamber in the boiler which then conveys it to the bottom of the collector. At this point the process restarts; there is no need for any pump for as long as the boiler stays above the panel/s. This process starts and stops by itself, with the presence of the heat (sun).

b. Forced circulation: instead of having the fluid moving by itself following the laws of thermodynamics, the fluid is pumped through the panels and the closed circuit by a small electric pump. An electronic control system will make sure that the circulation of the fluid continues for as long as the fluid temperature in the panel is higher than the one in the boiler. This system is used when the boiler is installed below the panel/s.