Solar heater working principle
The solar heater works through special panels that collect solar energy, which are specially made for that, and placed on a sufficient area of the roof of the house, and this energy is used to heat the water in it, as solar water heating can provide 50-80% of the needs of the house From hot water,  the heating process begins when sunlight strikes the collector to heat the water inside, and the circulating pump, which is regulated by the PV panel, begins to rotate during the activity of the photovoltaic panel by the amount of absorbed solar energy, then the DC propulsion pump moves the water from the tank through the collector Then return to the tank again. 
The sun changes during the day and the speed of the pump changes accordingly, and at the end of the day the process of passing water from the collector to the tank and vice versa has been repeated a lot, so that all the water in the tank becomes hot and usable immediately, but in the event that the periodic pump is organized by an electronic control unit Then, the sensor at the outlet of the collector activates the pump when the water temperature is between 15-20 degrees Fahrenheit, which is warmer than the water at the bottom of the tank, and thus the pump distributes the water to the collector, and the process continues when the water temperature is The collecting port is 5 degrees Fahrenheit higher than the water at the bottom of the tank, and if the temperature drops further, the control unit shuts off the pump automatically. 
Active solar heater systems
Active systems are one of the solar heater systems, in which mechanical pumps and control units are used to regulate the flow of heat-carrying water from the solar collector to the tank, where these control devices control the temperature difference between the tank and the solar collector, and the pump is switched when The water in the tank cools and reaches a lower temperature than the temperature of the collector, and some pumps work depending on electricity directly, while others work on the electricity that is generated from the solar photovoltaic panel, and there are some systems that work with solar energy, where liquids move in them when they fall The sun’s rays are used, so that the water is stored in insulated tanks to maintain its temperature during the night periods. Electricity may sometimes be used on cloudy days, when the sun’s rays are shielded.
Passive systems for solar heaters
Passive systems depend on gravity instead of using electricity, which is more efficient in areas with a hot climate, due to the absence of freezing at night or in the winter, where the passive system depends on the heat flow, when cold water flows due to gravity The solar collector, this water passes through the collector to raise its temperature through the phenomenon of convection, and then it reaches the water tank. 
Video Shows how the solar heater working