In this paper, a system of equations for the heat transfer of flat solar collectors (vertical plates) in a free air flow was solved. As a test example, all possible sizes of collectors were used, while the prototype was tested within 3-8% relative to the standardized standard deviation. Thermal characteristics decrease almost linearly as the distance between the pipes increases. This highlights the difficulty of transferring heat to the pipe from relatively long distances. This indicates the fact that a higher saturation of the tube per square unit (or length) of the absorbing plate increases its thermal efficiency. An increase in the mass flow rate of water circulating through the collector pipes will contribute to the greatest heat exchange, which will positively affect the efficiency of the system. As a result of the study, the actual daily increase in heat generation was about 800 MJ at various ambient temperatures. In temperature criteria, the greatest significance of the daily performance of the system was 48% with a small temperature difference between the collectors and the environment.