Solar water heating (SWH) is the conversion of sunlight into renewable energy for water heating using a solar thermal collector. Solar water heating systems comprise various technologies that are used worldwide increasingly.
Evacuated Tube is the core of the solar water heater, its structure as an elongated thermos bottle, a vacuum between the inner and outer layers. On the inner surface of the glass tube is coated with a spectrally selective absorbing coating, there is a NTC temperature sensor under the coating which is used to measure the maximum absorption of solar radiation. By sunlight, photon hits the coating, solar energy turn into heat energy.
Water absorbs heat from the outside coating, the water temperature is increase and the density is decrease, hot water upward movement, in this process, the temperature measurement is very important, so the temperature sensor is the important component to the solar water heating.