Salt gradient solar ponds

Salt-Gradient Solar Ponds and Their Liner Requirements... 

A schematic diagram of a salt-gradient solar pond is shown in Figure 1. It is a pond in which salt has been dissolved, in high concentrations near the bottom, and decreasing to low concentrations near the surface. Sodium chloride is the most commonly used salt, although there are numerous other possibilities. 

Figure 1. Cross-section of a salt gradient solar pond.

A salt-gradient solar pond was constructed in 1975 at the the Ohio Agricultural Research and Development Center in Wooster, Ohio ( ). The first liner, a chlorinated polyethylene liner, 50 mil in thickness, failed on filling of the pond. It was replaced by a second liner of the same material which failed two years later in 1977. The third liner, Shelter-Rite XR-5, has been in use since August 1977 and continues in service. 

Nielsen, C. E. "Nonconvective salt gradient solar ponds." Marcel Dekker, New York, 1980. 

Flexible Membrane Linings for Salt-Gradient Solar Ponds... 

This combination of easy seaming and repairs, outstanding weathering—fully exposed, and performance in high-temperature, high-concentration brine solutions makes Hypalon a prime candidate for lining salt-gradient solar ponds. 

Wishful thinking No - such a system does exist, and is being developed commercially. The most complicated thing about the system is its name - Non-convective Salt Gradient Solar Pond. (Figure 1)... 

Figure 1. Salt gradient solar pond. (Reproduced with permission from Ref. 1. Copyright 1980, Solar Energy Research Institute.)...

Salt gradient solar ponds present special problems frequently encountered in combination. They Include ... 

The location of a sizable volume of salt brine in most areas presents a potential for serious contamination. Leakage of brine from a damaged liner can "poison" the soil and the ground water over a wide area, if not promptly repaired. Proper selection of the impermeable liner is essential to wide-spread use of salt gradient solar ponds. 

Many of the lining materials commonly used for liquid storage cannot be used in salt gradient solar ponds. Compacted soils, native clays, soil additives or soil cement, swelling clays such as Bentonite, are not Impermeable to high temperature saturated salt brine solutions. Only the flexible membrane lining materials offer the potential for impermeability (zero leakage)... 

Salt gradient solar pond technology has largely been developed within the last five (5) years. Very few conmerclal installations exist even today, so that little comprehensive Information about flexible membrane liners has been developed. 

The Initial use of hypalon as a liner for a salt gradient solar pond came about strictly as an accident. 

The non-convective salt gradient solar pond will not vaporize metals, flash steam or power your car or watch. Its advantages are significant, however ... 

The use of an Impermeable flexible membrane liner will allow salt gradient solar ponds to be located near the energy user, by preventing salt contamination of the soil and ground water. 

Zangandro, F., "Observation and Analysis of a Full-Scale Experimental Salt Gradient Solar Pond", Doctorate Thesis, University of New Mexico, May, 1979. 

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