Movement of water without a pump!
This solar water heater does not have a pump. The flow of water between the storage tank and the collector happens all by itself, by a process called convection. As the water in the solar collectors gets hot, it gets lighter and moves upwards and into the storage tank at the right hand side. The coldest water in the storage tank falls downwards and to the left where it gets pushed out and into the collector panels. Once in the collector panels it gets heated up again and keeps going in a circle. This behaviour is called thermo-syphoning!
Cold water is heavier than hot water, so cold water sinks to the bottom of the tank. Hot water from the collector panel enters the storage tank from the inlet on the top right, and cold water exits the tank and flows into the collector panel from the outlet on the lower left of the tank.