Electric Power from Saline Solar Ponds

A solar saline pond is a few meters in depth and artificially maintained so that the degree of its salinity, and consequently density, is higher at the bottom than at the surface. The difference in salinity is created by dissolving large amounts of salt at the bottom of the pond and keeping the surface supplied with low-saline water, to maintain the necessary salinity gradient. Because of the difference in salinity there is minimal mixing between the layers, and convection is prevented. Absorption of solar energy by the bottom of the pond heats the lower depths of water, which are prevented from rising by higher density relative to upper part of the pond. Under these conditions, water at the bottom of the pond can attain temperatures close to 90 °C. Research on saline solar ponds began in the 1950s in Israel, and resulted in the early 1980s in the construction of a 25-hectare demonstration plant in Beit Ha'aravah near the Dead Sea [59]. A 5-MW low-temperature turbine using a low-boiling working fluid was used to transform the temperature difference between the pond's water layers into electricity. The overall efficiency of such a relatively low-temperature system was only about 1%. On a continuous basis, the pond provided approximately 800 kW. The unique feature of the saline pond, however, is that it can store the energy of the Sun in the form of heat and provide electricity even at night and during cloudy days. The Israeli solar saline pond power plant was operated until 1990. Since then, only one other plant using this technology has been built in Texas to provide a food cannery with both electricity and heat. Due to the relatively low efficiency of the system and the large area of land required, the potential of energy production from solar saline ponds is, however, limited.

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