Solar water heaters -- also called solar domestic hot water systems -- can be a cost-effective way to generate hot water for your home. Just like any other big purchases made for your home, its important when buying a solar geyser that you understand what you’re paying for, and how it will benefit you in the long run. They can be used in any climate, and the fuel they use -- sunshine -- is free. Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.
There are two types of active solar water heating systems:
Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes. The water moves through the solar collector and then directly into the geyser with the assistance of electrical pumps and controls. If not, it can be done via a natural thermosiphoning
Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures. Unlike the direct solar water geyser, the indirect solar water geyser has a solar collector that transfers a heat transfer fluid such as antifreeze. Thereafter, the antifreeze flows through the heat exchanger, which is surrounded by water. The water receives the heat from the antifreeze (but never mixes with it).
Internal workings of solar water geysers
Solar water geysers rely on warm water rising, better known as convection. This is how water circulates through the panels. Convection happens when the water stored in the panels heats up and rises into the water tank above, or in the ceiling – depending on where you decide to install it. The hot water in the tank then moves into the cylinder, usually located inside the house.
Meanwhile, the cooler water in the tanks flows downwards into the absorber (collector). These actions create circulation.
If the solar geyser is in the ceiling and at a lower level than the panels outside on the roof, then convection will not take place and a circulating pump is required to circulate the water between the tank and panels.