Household solar water heaters usually work in a natural cycle, with no external power. Vacuum tubular Solar water heater is a straight-plug structure, hot water through the action of gravity to provide power. Flat-panel Solar water heaters provide power through the pressure of tap water, known as topping. And the solar central heating system all use pump cycle. Due to the small heat collection area of solar water heater, the pipeline circulation is generally not used in view of the loss of heat energy.