SunRise Series Direct-plug solar water heater

Glass vacuum tubes absord energy from sunlight, and transfer the sunlight thermal to water in tubes , then the water temperature go up and hot water rise to tank , cold water in tank go down , circulation like so one day , the cold water in Tank become hot water, when the tank is empty , the user should open the input valve to let the cold water fill the tank , when overflow have cold water go out ,which means the tank is full,then user close the input valve.