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<br />, <br /> <br />\ <br />",; <br /> <br />w <br />c.n <br />~ <br />c.,., <br /> <br />u,-t. I C(}(l <br /> <br />SOLAR PONDS <br /> <br />"The status of solar ponds today roughly parallels that ---- of all solar <br /> <br /> <br />technology in the early 1970's" (Introduction to National Solar Pond <br /> <br />Program Plan, July, 1980). <br /> <br />What is a Salt Gradient Solar Pond? <br /> <br />A solar pond is a body of still water that captures solar radiation and <br /> <br />stores it as usable heat. This thermal energy then can be used for a <br /> <br /> <br />variety of purposes, including industrial process heat and electrical power <br /> <br /> <br />generation (see Figure 1). <br /> <br />When solar radiation penetrates a body of water, it is absorbed and causes <br /> <br /> <br />the water temperature to increase. In a normal body of water, the increase <br /> <br /> <br />in temperature causes the water to expand slightly, rise to the top and <br /> <br /> <br />dissipate heat to the atmosphere. This heat transfer mechanism is known as <br /> <br /> <br />natural convection. <br /> <br />In a salt gradient solar pond, a salt concentration gradient is artifi- <br /> <br />cially created whereby salinity and therefore density increase with <br /> <br />depth. The increase in density prevents heated natural convection. Heat <br /> <br />also can be lost through radiation and conduction. But because water is <br /> <br /> <br />opaque to the far-infrared range of solar radiation and still water has <br /> <br />relatively poor thermal conductivity, solar energy absorbed in the pond <br /> <br />virtually is trapped. <br /> <br />A non-convective solar pond provides the three main elements of any solar <br /> <br />thermal power system: collecting, storing, and cooling. The lower layer of <br /> <br />-1- <br /> <br />1 <br />,I <br />