The thermosiphon effect is a circular thermic movement in which the higgest the temperature difference is between the water in the collector and the water that is stored in the tank, the faster the water will flow through the circuit.
Operation
The thermosiphon effect is a circular thermic movement in which, the bigger is the temperature difference between the water in the collector and the water that is stored in the tank, the faster the water flows through the circuit.
As the sun heats the collector, the stored water increases it's temperature, decreases it's specific weight and becomes lighter; that way it goes up to the top of the tank, while the cold water, which is heavier, goes down to the bottom of the collector where it begins to increase its temperature.
The water cycle is natural, and there is no need for a pump.