In the time when the sun is not shining, the system is inactive and the solar water is hold in the drain-back tank. The system is controlled by a control unit and two temperature sensors.
Now, when the sun comes out and shining on the collector and the outside temperature sensor, the temperature compared with the personally desired temperature (e.g., 30°C). The control unit determines from the two sensors that the pool water temperature is lower than the 30°C and the outside temperature is higher than the pool water.
Now the solar pump (circulating pump) switches on and pumps the water from the drain-back tank into the collectors.
SAFE - LOW-MAINTENANCE - COST-EFFECTIVE