How does a solar water heater work?

Solar water heaters are used to convert solar energy into heat and then use the heat to warm up the water. Solar water heaters are mostly used for residential and some industrial applications. 

Solar water heaters or SWH are active and passive. Water heaters may use both water and heating fluid or both together. In an actively driven SWH, the systems use one or more pumps to circulate water and/or heating fluid.

This allows the system for a wide range of configuration. Whereas, in a passive SWH, the system uses tanks which serve both as storage and collector.

A solar water heater consists of four main components which together perform the process of water heating using the solar energy.

• Collector: Solar thermal collectors are used to capture the heat from the sun and retain it so that it can be used to heat a liquid. The collectors are also designed to minimize the heat loss. There are two types of collectors. One is flat plate collector and the other is evacuated tube. Both types of collectors are helpful in capturing the heat to use it for water heating.
• Pump: Pump is used to pass the water through the solar heater. Photovoltaic pump or PV pump uses a photovoltaic panel to power the active system. Another type of pump is bubble pump which reduces the pressure allowing the water to boil at low temperature.
• Controller: A controller helps to watch the temperature distinctions between the water pumped from the collector and from the storage tank. It starts the pump when the water becomes about 8-10 °C warmer than the water in the tank.
• Tank:  The tank in SWH is thermally insulated by a glass-topped box encasing the tank which allows heat from the sun to reach the tank. The walls of the tank are also thermally insulated, reducing convection and radiation.