When a liquid is heated it expands, becoming less dense and therefore more buoyant than cooler liquid, so it rises to the top. This is of course 'convection' – a principle that is utilised most effectively in a thermosyphon solar system.
As the liquid at the bottom of the solar panels is heated by the sun, it rises through a system of copper pipes, gaining heat all the time, and then flows into a jacket surrounding the water tank. The two liquids therefore never mix – the solar system is in fact a closed circuit, so the solar-heated liquid simply radiates (or 'exchanges') its heat to the domestic-use water inside the tank.
The solar-circuit liquid cools as it gives its heat, to be replaced by further warm water rising up from the panels below. Through this continuous cycle, the water in the tank gradually gains heat until it's hot enough for a bath or shower.
The basic working principle of solar water heating remains the same. A pressure pump is used to pump cold water from the source into the Water tank.
This type of water heating system is used when
- The level of the overhead tank (The original cold water source) is at low level.
- High pressure hot water flow is required for various uses like shower panels, jet shower, telephone shower, etc.
- The number of hot water points are more than normal.
The advantages of this system are
- Cold water wastage is not there.
- Hot water is readily available on the turn of the tap.
- Electricity is saved because wastage of cold water is minimized, thus saving precious resources.