Pool water is pumped through the collector gaining heat as it travels through the piping. A relatively large area of piping, typically half the surface area of the pool, is required due to the low thermal efficiency of the unglazed piping. Glazing the pipework, whilst increasing the thermal efficiency, is not cost effective as only a small temperature rise is required. When large amounts of low temperature heat is required other forms of solar heating, such as flat plate collectors are too expensive. For example, many industrial and agricultural applications requiring either low temperature heat or steam could utilise solar pond technology.
Solar ponds use the natural properties of salt water to collect and store heat energy.
The most common example of a solar pond is the salt gradient pond which consists of three differing concentrations of a salt solution, usually sodium or magnesium chloride. Dark coloured absorbing material is often used to line the pool to enhance the asborption of solar radiation and to prevent groundwater contamination. Sunlight is absorbed by the salty water and lining, heating the lower layers of the pond. Heat is extracted from this layer by pumping the salt solution from the bottom layer thorugh an external heat exchanger. Alternatively, a heat transfer fluid may be used pumped through a heat exchanger placed on the bottom of the pond.