solar water heater - UPSWH

Pre-heated solar water heater also relies on the natural circulation of water between the collector and the tank (that is tubes absorb solar energy,and heats the water inside the tube,hot water rises,cold water flows down).
It differs from compact non-pressurized solar water heater because it gets a copper coil inside the inner tank. The hot water rises from the tube into the tank, and heats the copper coil and finally heats the water inside the copper coil . Therefore the water tank is just as heat storage tank.