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. Membrane Ponds Membrane ponds behave in a similiar fashion to salt gradient ponds, except a thin transparent membrane is used to separate each of the layers of the pond.
Heat is removed from the pond using the same technology as salt gradient ponds.
Solar Pond Technology Israel leads the way in the development of solar pond technology, although several developing nations are also investigating solar ponds for providing low temperature heat requirements for industrial processes. Several demonstration projects are operational in the United States of America, including a salt gradient pond used for recreational building and pool heating and a 5MW system at Beit Ha'Arava, Israel. Except for solar water heating for hot water services and pools, very little research, development and demonstration of low temperature solar thermal technologies is occuring in Australia. Much of what is occuring is one off projects, such as the solar pond research at Centre for Water Resources in Western Australia, or the result of dedicated enthusiasts in areas such as solar cooking. Oxford University Press, Oxford.