Solar water heaters are usually found in a wide range of varieties today. These varieties are made of different designs which are composed of a collector and a storage tank. They normally use the sun as the main source of energy to heat water to be used for various purposes by human beings. In order to get their mode of operation, solar water heaters should be described according to the mode of collector and the circulation systems. There are various collector systems that are found in solar water heaters today.

Batch collector is one of the commonly found collector systems today. This is used in heating of water in dark tanks within insulated boxes and stores water until morning. With this kind of collector, water can stay in the day long even when the demand is low; and due to this, the water becomes hotter. It has a tempering valve which is used in mixing of cold water before being delivered to the taps. This kind of collector is not usually advised for use especially in cold climate since it is not compatible with closed-loop circulation systems. Another mode of collector is the flat rate which entails the copper tubes fitted on a flat absorber plates. With this type of collector, the common configuration entails series of parallel tubes joined at each end by two pipes which are the inlet and outlet manifolds. It is mainly designed in serving a family of four which is so convenient for persons with few members in a particular household.

An evacuated tube collector is another mode used for solar water heaters today. it is quite expensive as compared to a flat rate collector. According to many reviewers, it is rated to be the most efficient of all types of collectors found in the market. There is less heat lost in this collector since it is surrounded by a large glass tube and the space between them is a vacuum. Usually, its systems are capable of operating in temperatures that are forty and below and also works well in over cast conditions. Apart from the collectors' types, the solar water heater is also determined by the type of circulation systems it uses. For example, there is a direct system which is used to circulate water through the solar collectors through heating via the sun. Once the water is heated, it can be used directly or transferred through another tank where it can be used according to the demand by the given persons. Mostly, the direct means is preferred in areas where there is no freezing. On the other hand, we have an indirect circulation system. This kind of systems uses a non-freezing liquid to ensure transfer of heat from the sun to the water storage tank. The fluid is first heated by the sun; then, it passes to the heat exchanger in the storage tank where it transfers heat to the water. In case of a non-freezing fluid, it is passed back to the cycle for the same process hence making the method suitable for areas that have freezing climates.

The other types of the circulation systems are the active and passive methods. Active is associated with the use of electric means in heating of the water unlike in passive where it does not require pumps. A solar water heating pump is therefore convenient when the above two essentials are involved since they help in making the work easier and efficient in operation. It should be noted, therefore, that solar water heaters work best with collectors and good circulation systems depending on the preference of a particular individual.